Journal Articles

To date, 55 journal articles have been published. They are listed below in reverse chronological order.

2024
Title
Depth-resolved Characterization of Meissner Screening Breakdown in Surface Treated Niobium
Author
E. Thoeng, M. Asaduzzaman, P. Kolb, R. M. L. McFadden, G. D. Morris, J. O. Ticknor, S. R. Dunsiger, V. L. Karner, D. Fujimoto, T. Junginger, R. F. Kiefl, W. A. MacFarlane, R. Li, S. Saminathan, R. E. Laxdal
Journal
Scientific Reports
Volume
14
Issue
1
Pages
21487
Year
2024
Abstract
We report direct measurements of the magnetic field screening at the limits of the Meissner phase for two superconducting Nb samples. The samples are processed with two different surface treatments that have been developed for superconducting radio-frequency cavity applications - a "baseline" treatment and an oxygen-doping ("O-doping") treatment. The measurements show: 1) that the screening length is significantly longer in the "O-doping" sample compared to the "baseline" sample; 2) that the screening length near the limits of the Meissner phase increases with applied field; 3) the evolution of the screening profile as the material transitions from the Meissner phase to the mixed phase; and 4) a demonstration of the absence of any screening profile for the highest applied field, indicative of the full flux entering the sample. Measurements are performed utilizing the -detected nuclear magnetic resonance (β-NMR) technique that allows depth resolved studies of the local magnetic field within the first 100 nm of the surface. The study takes advantage of the β-SRF beamline, a new facility at TRIUMF, Canada, where field levels up to 200 mT are available parallel to the sample surface to replicate radio frequency (RF) fields near the Meissner breakdown limits of Nb.
10.1038/s41598-024-71724-5
arXiv:2405.05451 [cond-mat.supr-con]
2023
Title
Ion-implanted 8Li nuclear magnetic resonance in highly oriented pyrolytic graphite
Author
J. O. Ticknor, J. Adelman, A. Chatzichristos, M. H. Dehn, L. Egoriti, D. Fujimoto, V. L. Karner, R. F. Kiefl, C. D. P. Levy, R. Li, R. M. L. McFadden, G. D. Morris, M. R. Pearson, M. Stachura, E. Thoeng, W. A. MacFarlane
Journal
Physical Review B
Volume
108
Issue
19
Pages
195437
Year
2023
Abstract
We report β-detected nuclear magnetic resonance of ultra-dilute 8Li+ implanted in highly oriented pyrolytic graphite (HOPG). The absence of motional narrowing and diffusional spin-lattice relaxation implies Li+ is not appreciably mobile up to 400 K, in sharp contrast to the highly lithiated stage compounds. However, the relaxation is remarkably fast and persists down to cryogenic temperatures. Ruling out extrinsic paramagnetic impurities and intrinsic ferromagnetism, we conclude the relaxation is due to paramagnetic centers correlated with implantation. While the resulting effects are not consistent with a Kondo impurity, they also differ from free paramagnetic centers, and we suggest that a resonant scattering approach may account for much of the observed phenomenology.
10.1103/PhysRevB.108.195437
arXiv:2301.07821 [cond-mat.mtrl-sci]
Title
Depth-resolved Meissner screening in a niobium thin film from spin-lattice relaxation of the implanted β-emitter 8Li
Author
R. M. L. McFadden, M. Asaduzzaman, T. J. Buck, D. L. Cortie, M. H. Dehn, S. R. Dunsiger, R. F. Kiefl, R. E. Laxdal, C. D. Philip Levy, W. A. MacFarlane, G. D. Morris, M. R. Pearson, E. Thoeng, T. Junginger
Journal
Journal of Applied Physics
Volume
134
Issue
16
Pages
163902
Year
2023
Abstract
We report measurements of the Meissner screening profile in a Nb(300 nm)/Al2O3 thin film using 8Li β-detected nuclear magnetic resonance (β-NMR). The NMR probe 8Li was ion-implanted into the Nb film at energies ≤ 20 keV, corresponding to mean stopping depths comparable to Nb's magnetic penetration depth λ. 8Li's strong dipole-dipole coupling with the host 93Nb nuclei provided a "cross-relaxation" channel that dominated in low magnetic fields, which conferred indirect sensitivity to the local magnetic field via the spin-lattice relaxation (SLR) rate 1/T1. From a fit of the 1/T1 data to a model accounting for its dependence on temperature, magnetic field, and 8Li+ implantation energy, we obtained a magnetic penetration depth λ0 = 51.5(22) nm, consistent with a relatively short carrier mean-free-path ℓ = 18.7(29) nm typical of similarly prepared Nb films. The results presented here constitute an important step towards using 8Li β-NMR to characterize bulk Nb samples with engineered surfaces, which are often used in the fabrication of particle accelerators.
10.1063/5.0175532
arXiv:2212.01137 [cond-mat.mtrl-sci]
Title
A new high parallel-field spectrometer at TRIUMF's β-NMR facility
Author
E. Thoeng, R. M. L. McFadden, S. Saminathan, G. D. Morris, P. Kolb, B. Matheson, M. Asaduzzaman, R. Baartman, S. R. Dunsiger, D. Fujimoto, T. Junginger, V. L. Karner, S. Kiy, R. Li, M. Stachura, J. O. Ticknor, R. F. Kiefl, W. A. MacFarlane, R. E. Laxdal
Journal
Review of Scientific Instruments
Volume
94
Issue
2
Pages
023305
Year
2023
Abstract
A new high field spectrometer has been built to extend the capabilities of the β-detected nuclear magnetic resonance (β-NMR) facility at TRIUMF. This new beamline extension allows β-NMR spectroscopy to be performed with fields up to 200 mT parallel to a sample's surface (perpendicular to the ion beam), allowing depth-resolved studies of local electromagnetic fields with spin polarized probes at a much higher applied magnetic field than previously available in this configuration. The primary motivation and application is to allow studies of superconducting radio frequency (SRF) materials, close to the critical fields of Nb metal, which is extensively used to fabricate SRF cavities. The details of the design considerations and implementation of the ultra-high vacuum (UHV) system, ion optics, beam diagnostics are presented here. Commissioning of the beamline and spectrometer with radioactive ions are also reported here. Future capabilities and applications in other areas are also described.
10.1063/5.0137368
arXiv:2211.15619 [cond-mat.mtrl-sci]
2022
Title
Nuclear magnetic resonance of 8Li ions implanted in ZnO
Author
J. R. Adelman, D. Fujimoto, M. H. Dehn, S. R. Dunsiger, V. L. Karner, C. D. P. Levy, R. Li, I. McKenzie, R. M. L. McFadden, G. D. Morris, M. R. Pearson, M. Stachura, E. Thoeng, J. O. Ticknor, N. Ohashi, K. M. Kojima, W. A. MacFarlane
Journal
Physical Review B
Volume
106
Issue
3
Pages
035205
Year
2022
Abstract
We report on the stability and magnetic state of ion implanted 8Li in single crystals of the semiconductor ZnO using β-detected nuclear magnetic resonance. At ultradilute concentrations, the spectra reveal distinct Li sites from 7.6 to 400 K. Ionized shallow donor interstitial Li is stable across the entire temperature range, confirming its ability to self-compensate the acceptor character of its (Zn) substitutional counterpart. Above 300 K, spin-lattice relaxation indicates the onset of correlated local motion of interacting defects, and the spectra show a site change transition from disordered configurations to substitutional. Like the interstitial, the substitutional shows no resolved hyperfine splitting, indicating it is also fully ionized above 210 K. The electric field gradient at the interstitial 8Li exhibits substantial temperature dependence with a power law typical of non-cubic metals.
10.1103/PhysRevB.106.035205
arXiv:2109.08637 [cond-mat.mtrl-sci]
Title
Magnesium(II)-ATP complexes in 1-ethyl-3-methylimidazolium acetate solutions characterized by 31Mg β-radiation-detected NMR spectroscopy
Author
R. M. L. McFadden, D. Szunyogh, N. Bravo-Frank, A. Chatzichristos, M. H. Dehn, D. Fujimoto, A. Jancsó, S. Johannsen, I. Kálomista, V. L. Karner, R. F. Kiefl, F. H. Larsen, J. Lassen, C. D. P. Levy, R. Li, I. McKenzie, H. McPhee, G. D. Morris, M. R. Pearson, S. P. A. Sauer, R. K. O. Sigel, P. W. Thulstrup, W. A. MacFarlane, L. Hemmingsen, M. Stachura
Journal
Angewandte Chemie International Edition
Volume
61
Issue
35
Pages
e202207137
Year
2022
Abstract
The complexation of MgII with adenosine 5'-triphosphate (ATP) is omnipresent in biochemical energy conversion, but is difficult to interrogate directly. Here we used the spin-1/2 β-emitter 31Mg to study MgII-ATP complexation in 1-ethyl-3-methylimidazolium acetate (EMIM-Ac) solutions using β-radiation-detected nuclear magnetic resonance (β-NMR). We demonstrate that (nuclear) spin-polarized 31Mg, following ion-implantation from an accelerator beamline into EMIM-Ac, binds to ATP within its radioactive lifetime before depolarizing. The evolution of the spectra with solute concentration indicates that the implanted 31Mg initially bind to the solvent acetate anions, whereafter they undergo dynamic exchange and form either a mono- (31Mg-ATP) or di-nuclear (31MgMg-ATP) complex. The chemical shift of 31Mg-ATP is observed up-field of 31MgMg-ATP, in accord with quantum chemical calculations. These observations constitute a crucial advance towards using β-NMR to probe biologically relevant contexts.
10.1002/anie.202207137
Title
Repeatable photoinduced insulator-to-metal transition in yttrium oxyhydride epitaxial thin films
Author
Y. Komatsu, R. Shimizu, R. Sato, M. Wilde, K. Nishio, T. Katase, D. Matsumura, H. Saitoh, M. Miyauchi, J. R. Adelman, R. M. L. McFadden, D. Fujimoto, J. O. Ticknor, M. Stachura, I. McKenzie, G. D. Morris, W. A. MacFarlane, J. Sugiyama, K. Fukutani, S. Tsuneyuki, T. Hitosugi
Journal
Chemistry of Materials
Volume
34
Issue
8
Pages
3616-3623
Year
2022
Abstract
Currently, no known material retains its photoinduced metallic conductivity over a long time while also exhibiting repeatable metal-to-insulator recovery. Here, we demonstrate such a highly repeatable photoinduced insulator-to-metal transition in yttrium oxyhydride (YOxHy) epitaxial thin films. The temperature (T) dependence of the electrical resistivity (ρ) of the films transforms from the insulating to the metallic state (dρ/dT > 0) under ultraviolet laser illumination. The YOxHy film recovers its original insulating state when heated (125 °C) under an Ar atmosphere and regains metallic conductivity when subsequently subjected to ultraviolet laser illumination again, showing a repeatable photoinduced insulator-to-metal transition. First-principles calculations show that the itinerant carriers originate from the variations in the charge states of the hydrogen atoms that occupy octahedral interstitial sites. This study indicates that tuning the site occupancy (octahedral/tetrahedral) of the hydrogen atoms exerts a significant effect on the photoresponse of metal hydrides.
10.1021/acs.chemmater.1c03450
Title
A β-NMR study of the depth, temperature, and molecular-weight dependence of secondary dynamics in polystyrene: Entropy–enthalpy compensation and dynamic gradients near the free surface
Author
I. McKenzie, D. Fujimoto, V. L. Karner, R. Li, W. A. MacFarlane, R. M. L. McFadden, G. D. Morris, M. R. Pearson, A. N. Raegan, M. Stachura, J. O. Ticknor, J. A. Forrest
Journal
The Journal of Chemical Physics
Volume
156
Issue
8
Pages
084903
Year
2022
Abstract
We investigated the depth, temperature, and molecular-weight (MW) dependence of the γ-relaxation in polystyrene glasses using implanted 8Li+ and β-detected nuclear magnetic resonance. Measurements were performed on thin films with MW ranging from 1.1 to 641 kg/mol. The temperature dependence of the average 8Li spin–lattice relaxation time (T1avg) was measured near the free surface and in the bulk. Spin–lattice relaxation is caused by phenyl ring flips, which involve transitions between local minima over free-energy barriers with enthalpic and entropic contributions. We used transition state theory to model the temperature dependence of the γ-relaxation, and hence T1avg. There is no clear correlation of the average entropy of activation (Δ‡S̄) and enthalpy of activation (Δ‡H̄) with MW, but there is a clear correlation between Δ‡S̄ and Δ‡H̄, i.e., entropy–enthalpy compensation. This results in the average Gibbs energy of activation, Δ‡Ḡ, being approximately independent of MW. Measurements of the temperature dependence of T1avg as a function of depth below the free surface indicate the inherent entropic barrier, i.e., the entropy of activation corresponding to Δ‡H̄ = 0, has an exponential dependence on the distance from the free surface before reaching the bulk value. This results in Δ‡Ḡ near the free surface being lower than the bulk. Combining these observations results in a model where the average fluctuation rate of the γ-relaxation has a “double-exponential” depth dependence. This model can explain the depth dependence of 1/T1avg in polystyrene films. The characteristic length of enhanced dynamics is ~6 nm and approximately independent of MW near room temperature.
10.1063/5.0081185
2021
Title
Evolution of the metallic state of LaNiO3/LaAlO3 superlattices measured by 8Li β-detected NMR
Author
V. L. Karner, A. Chatzichristos, D. L. Cortie, D. Fujimoto, R. F. Kiefl, C. D. P. Levy, R. Li, R. M. L. McFadden, G. D. Morris, M. R. Pearson, E. Benckiser, A. V. Boris, G. Cristiani, G. Logvenov, B. Keimer, W. A. MacFarlane
Journal
Physical Review B
Volume
104
Issue
20
Pages
205114
Year
2021
Abstract
Using ion-implanted 8Li β-detected NMR, we study the evolution of the correlated metallic state of LaNiO3 in a series of LaNiO3/LaAlO3 superlattices as a function of bilayer thickness. Spin-lattice relaxation measurements in an applied field of 6.55 T reveal two equal amplitude components: one with metallic (T linear) 1/T1, and a second with a more complex T-dependence. The metallic character of the slow relaxing component is only weakly affected by the LaNiO3 thickness, while the fast component is much more sensitive, exhibiting the opposite temperature dependence (increasing towards low T) in the thinnest, most magnetic samples. The origin of this bipartite relaxation is discussed in terms of electronic phase separation.
10.1103/PhysRevB.104.205114
arXiv:2106.00211 [cond-mat.str-el]
Title
bfit: a Python application for beta-detected NMR
Author
D. Fujimoto
Journal
Journal of Open Source Software
Volume
6
Issue
65
Pages
3598
Year
2021
Abstract
Beta-detected nuclear magnetic resonance (β-NMR) measures the beta-decay of probe radioactive nuclei to infer the electromagnetic character of the probe’s local environment. Similar to muon spin rotation (μSR), this technique allows for unique insight of material properties not easily measured by conventional NMR. The bfit package provides a graphical user interface (GUI) and application programming interface (API) to facilitate the analysis of implanted-ion β-NMR measurements taken at TRIUMF.
10.21105/joss.03598
2020
Title
Local electronic and magnetic properties of the doped topological insulators Bi2Se3:Ca and Bi2Te3:Mn investigated using ion-implanted 8Li β-NMR
Author
R. M. L. McFadden, A. Chatzichristos, D. L. Cortie, D. Fujimoto, Y. S. Hor, H. Ji, V. L. Karner, R. F. Kiefl, C. D. P. Levy, R. Li, I. McKenzie, G. D. Morris, M. R. Pearson, M. Stachura, R. J. Cava, W. A. MacFarlane
Journal
Physical Review B
Volume
102
Issue
23
Pages
235206
Year
2020
Abstract
We report β-detected nuclear magnetic resonance (β-NMR) measurements in Bi2Se3:Ca (BSC) and Bi2Te3:Mn (BTM) single crystals using 8Li+ implanted to depths on the order of 100 nm. Above ~200 K, spin-lattice relaxation (SLR) reveals diffusion of 8Li+, with activation energies of ~0.4 eV (~0.2 eV) in BSC (BTM). At lower temperatures, the nuclear magnetic resonance (NMR) properties are those of a heavily doped semiconductor in the metallic limit, with Korringa relaxation and a small, negative, temperature-dependent Knight shift in BSC. From this, we make a detailed comparison with the isostructural tetradymite Bi2Te2Se (BTS) [McFadden et al., Phys Rev. B 99, 125201 (2019)]. In the magnetic BTM, the effects of the dilute Mn moments predominate, but remarkably the 8Li signal is not wiped out through the magnetic transition at 13 K, with a prominent critical peak in the SLR that is suppressed in a high applied field. This detailed characterization of the 8Li NMR response is an important step towards using depth-resolved β-NMR to study the low-energy properties of the chiral topological surface state (TSS). With the bulk NMR response now established in several Bi2Ch3 tetradymite topological insulators (TIs), the prospect of directly probing their chiral TSS using the depth resolution afforded by β-NMR remains strong.
10.1103/PhysRevB.102.235206
arXiv:1911.12212 [cond-mat.mtrl-sci]
Title
Investigation of ionic and anomalous magnetic behavior in CrSe2 using 8Li β-NMR
Author
J. O. Ticknor, I. Umegaki, R. M. L. McFadden, A. Chatzichristos, D. Fujimoto, V. L. Karner, R. F. Kiefl, S. Kobayashi, C. D. P. Levy, R. Li, G. D. Morris, M. R. Pearson, K. Yoshimura, J. Sugiyama, W. A. MacFarlane
Journal
RSC Advances
Volume
10
Issue
14
Pages
8190-8197
Year
2020
Abstract
We have studied a mosaic of 1T-CrSe2 single crystals using β-detected nuclear magnetic resonance of 8Li from 4 to 300 K. We identify two broad resonances that show no evidence of quadrupolar splitting, indicating two magnetically distinct environments for the implanted ion. We observe stretched exponential spin lattice relaxation and a corresponding rate (1/T1) that increases monotonically above 200 K, consistent with the onset of ionic diffusion. A pronounced maximum in 1/T1 is observed at the low temperature magnetic transition near 20 K. Between these limits, 1/T1 exhibits a broad minimum with an anomalous absence of strong features in the vicinity of structural and magnetic transitions between 150 and 200 K. Together, the results suggest 8Li+ site occupation within the van der Waals gap between CrSe2 trilayers. Possible origins of the two environments are discussed.
10.1039/C9RA07065F
arXiv:1908.05421 [cond-mat.mtrl-sci]
2019
Title
Erratum: High resolution β-NMR study of 8Li+ implanted in gold [Physical Review B 77, 214107 (2008)]
Author
T. J. Parolin, Z. Salman, K. H. Chow, Q. Song, J. Valiani, H. Saadaoui, A. O’Halloran, M. D. Hossain, T. A. Keeler, R. F. Kiefl, S. R. Kreitzman, C. D. P. Levy, R. I. Miller, G. D. Morris, M. R. Pearson, M. Smadella, D. Wang, M. Xu, W. A. MacFarlane
Journal
Physical Review B
Volume
100
Issue
20
Pages
209904(E)
Year
2019
10.1103/PhysRevB.100.209904
Title
Dynamics of liquid 1-ethyl-3-methylimidazolium acetate measured with implanted-ion 8Li β-NMR
Author
D. Fujimoto, R. M. L. McFadden, M. H. Dehn, Y. Petel, A. Chatzichristos, L. Hemmingsen, V. L. Karner, R. F. Kiefl, C. D. P. Levy, I. McKenzie, C. A. Michal, G. D. Morris, M. R. Pearson, D. Szunyogh, J. O. Ticknor, M. Stachura, W. A. MacFarlane
Journal
Chemistry of Materials
Volume
31
Issue
22
Pages
9346-9353
Year
2019
Abstract
We demonstrate the application of implanted-ion β-detected NMR as a probe of ionic liquid molecular dynamics through the measurement of 8Li spin-lattice relaxation (SLR) and resonance in 1-ethyl-3-methylimidazolium acetate. The motional narrowing of the resonance and the local maxima in the SLR rate, 1/T1, imply sensitivity to subnanosecond Li+ solvation dynamics. From an analysis of 1/T1, we extract an activation energy EA = 74.8(1.5) meV and Vogel-Fulcher-Tammann constant TVFT = 165.8(0.9) K, in agreement with the dynamic viscosity of the bulk solvent. Near the melting point, the lineshape is broad and intense, and the form of the relaxation is nonexponential, reflective of our sensitivity to heterogeneous dynamics near the glass transition. The depth resolution of this technique may later provide a unique means of studying nanoscale phenomena in ionic liquids.
10.1021/acs.chemmater.9b02864
arXiv:1907.03684 [cond-mat.soft]
Title
Local metallic and structural properties of the strongly correlated metal LaNiO3 using 8Li β-NMR
Author
V. L. Karner, A. Chatzichristos, D. L. Cortie, M. H. Dehn, O. Foyevtsov, K. Foyevtsova, D. Fujimoto, R. F. Kiefl, C. D. P. Levy, R. Li, R. M. L. McFadden, G. D. Morris, M. R. Pearson, M. Stachura, J. O. Ticknor, G. Cristiani, G. Logvenov, F. Wrobel, B. Keimer, J. Zhang, J. F. Mitchell, W. A. MacFarlane
Journal
Physical Review B
Volume
100
Issue
16
Pages
165109
Year
2019
Abstract
We report β-detected NMR of ion-implanted 8Li in a single crystal and thin film of the strongly correlated metal LaNiO3. Spin-lattice relaxation measurements reveal two distinct local environments, both metallic as evident from T-linear Korringa 1/T1 below 200 K with slopes comparable to other metals. A small approximately temperature-independent Knight shift of ~74 ppm is observed, yielding a normalized Korringa product characteristic of substantial antiferromagnetic correlations. We find no evidence for a magnetic transition from 4 to 310 K. The similarity of these features in the two very different samples indicates that they are intrinsic and unrelated to dilute oxygen vacancies. We attribute the two environments to two distinct but similar crystallographic 8Li sites and not to any form of phase inhomogeneity, but this is inconsistent with the conventional rhombohedral structure of LaNiO3, and also cannot be simply explained by the common alternative orthorhombic or monoclinic distortions.
10.1103/PhysRevB.100.165109
arXiv:1906.07878 [cond-mat.str-el]
Title
Bi-Arrhenius diffusion and surface trapping of 8Li+ in rutile TiO2
Author
A. Chatzichristos, R. M. L. McFadden, M. H. Dehn, S. R. Dunsiger, D. Fujimoto, V. L. Karner, I. McKenzie, G. D. Morris, M. R. Pearson, M. Stachura, J. Sugiyama, J. O. Ticknor, W. A. MacFarlane, R. F. Kiefl
Journal
Physical Review Letters
Volume
123
Issue
9
Pages
095901
Year
2019
Abstract
We report measurements of the diffusion rate of isolated ion-implanted 8Li+ within ~120  nm of the surface of oriented single-crystal rutile TiO2 using a radiotracer technique. The α particles from the 8Li decay provide a sensitive monitor of the distance from the surface and how the depth profile of 8Li evolves with time. The main findings are that the implanted Li+ diffuses and traps at the (001) surface. The T dependence of the diffusivity is described by a bi-Arrhenius expression with activation energies of 0.3341(21) eV above 200 K, whereas at lower temperatures it has a much smaller barrier of 0.0313(15) eV. We consider possible origins for the surface trapping, as well the nature of the low-T barrier.
10.1103/PhysRevLett.123.095901
arXiv:1810.12537 [cond-mat.mtrl-sci]
Title
Ionic and electronic properties of the topological insulator Bi2Te2Se investigated via β-detected nuclear magnetic relaxation and resonance of 8Li
Author
R. M. L. McFadden, A. Chatzichristos, K. H. Chow, D. L. Cortie, M. H. Dehn, D. Fujimoto, M. D. Hossain, H. Ji, V. L. Karner, R. F. Kiefl, C. D. P. Levy, R. Li, I. McKenzie, G. D. Morris, O. Ofer, M. R. Pearson, M. Stachura, R. J. Cava, W. A. MacFarlane
Journal
Physical Review B
Volume
99
Issue
12
Pages
125201
Year
2019
Abstract
We report measurements on the high-temperature ionic and low-temperature electronic properties of the three-dimensional topological insulator Bi2Te2Se using ion-implanted 8Li β-detected nuclear magnetic relaxation and resonance. With implantation energies in the range 5-28 keV, the probes penetrate beyond the expected range of the topological surface state, but are still within 250 nm of the surface. At temperatures above ~150K, spin-lattice relaxation measurements reveal isolated 8Li+ diffusion with an activation energy EA = 0.185(8) eV and attempt frequency τ0−1 = 8 ± 3 × 1011 s-1 for atomic site-to-site hopping. At lower temperature, we find a linear Korringa-type relaxation mechanism with a field-dependent slope and intercept, which is accompanied by an anomalous field dependence to the resonance shift. We suggest that these may be related to a strong contribution from orbital currents or the magnetic freeze-out of charge carriers in this heavily compensated semiconductor, but that conventional theories are unable to account for the extent of the field dependence. Conventional NMR of the stable host nuclei may help elucidate their origin.
10.1103/PhysRevB.99.125201
arXiv:1810.07879 [cond-mat.mtrl-sci]
2018
Title
Direct observation of Mg2+ complexes in ionic liquid solutions by 31Mg β-NMR spectroscopy
Author
D. Szunyogh, R. M. L. McFadden, V. L. Karner, A. Chatzichristos, T. Day Goodacre, M. H. Dehn, L. Formenti, D. Fujimoto, A. Gottberg, E. Kallenberg, I. Kálomista, R. F. Kiefl, F. H. Larsen, J. Lassen, C. D. P. Levy, R. Li, W. A. MacFarlane, I. McKenzie, G. D. Morris, S. Pallada, M. R. Pearson, S. P. A. Sauer, P. Schaffer, P. W. Thulstrup, L. Hemmingsen, M. Stachura
Journal
Dalton Transactions
Volume
47
Issue
41
Pages
14431-14435
Year
2018
Abstract
NMR spectra of Mg2+ ions in ionic liquids were recorded using a highly sensitive variant of NMR spectroscopy known as β-NMR. The β-NMR spectra of MgCl2 in EMIM-Ac and EMIM-DCA compare favourably with conventional NMR, and exhibit linewidths of ~3 ppm, allowing for discrimination of species with oxygen and nitrogen coordination.
10.1039/C8DT02350F
Title
Direct measurements of the temperature, depth and processing dependence of phenyl ring dynamics in polystyrene thin films by β-detected NMR
Author
I. McKenzie, Y. Chai, D. L. Cortie, J. A. Forrest, D. Fujimoto, V. L. Karner, R. F. Kiefl, C. D. P. Levy, W. A. MacFarlane, R. M. L. McFadden, G. D. Morris, M. R. Pearson, S. Zhu
Journal
Soft Matter
Volume
14
Issue
36
Pages
7324-7334
Year
2018
Abstract
There is indirect evidence that the dynamics of a polymer near a free surface are enhanced compared with the bulk but there are few studies of how dynamics varies with depth. β-Detected nuclear spin relaxation of implanted 8Li+ has been used to directly probe the temperature and depth dependence of the γ-relaxation mode, which is due to phenyl rings undergoing restricted rotation, in thin films of atactic deuterated polystyrene (PS-d8) and determine how the depth dependence of dynamics is affected by sample processing, such as annealing, floating on water and the inclusion of a surfactant, and by the presence of a buried interface. The activation energy for the γ-relaxation process is lower near the free surface. Annealing the PS-d8 films and then immersing in water to mimic the floating procedure used to transfer films had negligible effects on the thickness of the region near the free surface with enhanced mobility. Measurements on a bilayer film indicate enhanced phenyl ring dynamics near the buried interface compared with a single film at the same depth. PS-d8 films annealed with the surfactant sodium dodecyl sulfate (SDS) deposited on the surface show enhanced dynamics in the bulk compared with a pure PS-d8 film and a PS-d8 film where the SDS was washed away. There is less contrast between the surface and bulk in the SDS-treated sample, which could account for the elimination of the Tg confinement effect observed in films containing SDS [Chen and Torkelson, Polymer, 2016, 87, 226].
10.1039/C8SM00812D
2017
Title
Microscopic dynamics of Li+ in rutile TiO2 revealed by 8Li β-detected nuclear magnetic resonance
Author
R. M. L. McFadden, T. J. Buck, A. Chatzichristos, C.-C. Chen, K. H. Chow, D. L. Cortie, M. H. Dehn, V. L. Karner, D. Koumoulis, C. D. P. Levy, C. Li, I. McKenzie, R. Merkle, G. D. Morris, M. R. Pearson, Z. Salman, D. Samuelis, M. Stachura, J. Xiao, J. Maier, R. F. Kiefl, and W. A. MacFarlane
Journal
Chemistry of Materials
Volume
29
Issue
23
Pages
10187-10197
Year
2017
Abstract
We report measurements of the dynamics of isolated 8Li+ in single crystal rutile TiO2 using β-detected nuclear magnetic resonance. From spin-lattice relaxation and motional narrowing, we find two sets of thermally activated dynamics: one below 100 K and one at higher temperatures. At low temperature, the activation barrier is 26.8(6) meV with prefactor 1.23(5) × 1010 s-1. We suggest this is unrelated to Li+ motion and rather is a consequence of electron polarons in the vicinity of the implanted 8Li+ that are known to become mobile in this temperature range. Above 100 K, Li+ undergoes long-range diffusion as an isolated uncomplexed cation, characterized by an activation energy and prefactor of 0.32(2) eV and 1.0(5) × 1016 s-1, respectively, in agreement with macroscopic diffusion measurements. These results in the dilute limit from a microscopic probe indicate that Li+ concentration does not limit the diffusivity even up to high concentrations but that some key ingredient is missing in the calculations of the migration barrier. The anomalous prefactors provide further insight into both Li+ and polaron motion.
10.1021/acs.chemmater.7b04093
arXiv:1709.06674 [cond-mat.mtrl-sci]
Title
Lithium diffusion in spinel Li4Ti5O12 and LiTi2O4 films detected with 8Li β-NMR
Author
J. Sugiyama, I. Umegaki, T. Uyama, R. M. L. McFadden, S. Shiraki, T. Hitosugi, Z. Salman, H. Saadaoui, G. D. Morris, W. A. MacFarlane, R. F. Kiefl
Journal
Physical Review B
Volume
96
Issue
9
Pages
094402
Year
2017
Abstract
Diffusion of Li+ in (111) oriented thin films of the spinels Li4Ti5O12 and LiTi2O4 has been studied with 8Li β-detected NMR in the temperature range between 5 and 310 K. In Li4Ti5O12, the spin-lattice relaxation rate (1/T1) versus temperature shows a clear maximum around 100 K (= Tmax) which we attribute to magnetic freezing of dilute Ti3+ local magnetic moments, consistent with the results of magnetization and muon spin relaxation (μ+SR) measurements. The decrease in 1/T1 with temperature above Tmax indicates that Li+ starts to diffuse with a thermal activation energy (Ea) of 0.11(1) eV. In LiTi2O4, on the contrary, as temperature increases from 200 K, 1/T1 increases monotonically up to 310 K. This suggests that Li also starts to diffuse above 200 K with Ea = 0.16(2) eV in LiTi2O4. Comparison with conventional Li-NMR on Li4Ti5O12 implies that both β-NMR and μ+SR sense short-range Li motion, i.e., a jump diffusion of Li+ to the nearest neighboring sites.
10.1103/PhysRevB.96.094402
Title
Determination of the nature of fluctuations using 8Li and 9Li β-NMR and spin-lattice relaxation
Author
A. Chatzichristos, R. M. L. McFadden, V. L. Karner, D. L. Cortie, C. D. P. Levy, W. A. MacFarlane, G. D. Morris, M. R. Pearson, Z. Salman, R. F. Kiefl
Journal
Physical Review B
Volume
96
Issue
1
Pages
014307
Year
2017
Abstract
We report a comparison of the 1/T1 spin-lattice relaxation rates for 9Li and 8Li in Pt and SrTiO3, in order to differentiate between magnetic and electric quadrupolar relaxation mechanisms. In Pt, the ratio of the 1/T1 spin relaxation rates RPt was found to be 6.82(29), which is close to but less than the theoretical limit of ~7.68 for pure magnetic relaxation. In SrTiO3 this ratio was found to be 2.7(3), which is close to but larger than the theoretical limit of ~2.14 expected for pure electric quadrupolar relaxation. These results bring insight into the nature of the fluctuations in the local environment of implanted 8Li observed by β-NMR.
10.1103/PhysRevB.96.014307
arXiv:1703.10156 [cond-mat.mtrl-sci]
Title
β-NMR measurements of molecular-scale lithium-ion dynamics in poly(ethylene oxide)-lithium-salt thin films
Author
I. McKenzie, D. L. Cortie, M. Harada, R. F. Kiefl, C. D. P. Levy, W. A. MacFarlane, R. M. L. McFadden, G. D. Morris, S.-I. Ogata, M. R. Pearson, J. Sugiyama
Journal
The Journal of Chemical Physics
Volume
146
Issue
24
Pages
244903
Year
2017
Abstract
β-detected NMR (β-NMR) has been used to study the molecular-scale dynamics of lithium ions in thin films of poly(ethylene oxide) (PEO) containing either lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium trifluoroacetate (LiTFA) salts at monomer-to-salt ratios (EO/Li) of 8.3. The results are compared with previous β-NMR measurements on pure PEO and PEO with lithium triflate (LiOTf) at the same loading [McKenzie et al., J. Am. Chem. Soc. 136, 7833 (2014)]. Activated hopping of 8Li+ was observed in all of the films above ~250 K, with the hopping parameters strongly correlated with the ionicity of the lithium salt rather than the polymer glass transition temperature. The pre-exponential factor increases exponentially with ionicity, while the activation energy for hopping increases approximately linearly, going from 6.3 ± 0.2 kJ mol-1 in PEO:LiTFA to 17.8 ± 0.2 kJ mol-1 in PEO:LiTFSI. The more rapid increase in the pre-exponential factor outweighs the effect of the larger activation energy and results in 8Li+ hopping being fastest in PEO followed by PEO:LiTFSI, PEO:LiOTf, and PEO:LiTFA.
10.1063/1.4989866
2016
Title
β-NMR investigation of the depth-dependent magnetic properties of an antiferromagnetic surface
Author
D. L. Cortie, T. Buck, M. H. Dehn, V. L. Karner, R. F. Kiefl, C. D. P. Levy, R. M. L. McFadden, G. D. Morris, I. McKenzie, M. R. Pearson, X. L. Wang, W. A. MacFarlane
Journal
Physical Review Letters
Volume
116
Issue
10
Pages
106103
Year
2016
Abstract
By measuring the prototypical antiferromagnet α−Fe2O3, we show that it is possible to determine the static spin orientation and dynamic spin correlations within nanometers from an antiferromagnetic surface using the nuclear spin polarization of implanted 8Li+ ions detected with β-NMR. Remarkably, the first-order Morin spin reorientation in single crystal α−Fe2O3 occurs at the same temperature at all depths between 1 and 100 nm from the (110) surface; however, the implanted nuclear spin experiences an increased 1/T1 relaxation rate at shallow depths revealing soft-surface magnons. The surface-localized dynamics decay towards the bulk with a characteristic length of ε = 11 ± 1  nm, closely matching the finite-size thresholds of hematite nanostructures.
10.1103/PhysRevLett.116.106103
2015
Title
β-detected NMR spin relaxation in a thin film heterostructure of ferromagnetic EuO
Author
W. A. MacFarlane, Q. Song, N. J. C. Ingle, K. H. Chow, M. Egilmez, I. Fan, M. D. Hossain, R. F. Kiefl, C. D. P. Levy, G. D. Morris, T. J. Parolin, M. R. Pearson, H. Saadaoui, Z. Salman, D. Wang
Journal
Physical Review B
Volume
92
Issue
6
Pages
064409
Year
2015
Abstract
We present β-detected NMR measurements of the spin-lattice relaxation of 8Li+ implanted into an epitaxial heterostructure based on a 100 nm thick film of ferromagnetic (FM) EuO as a function of temperature through its FM transition. In the FM state, the spin-lattice relaxation rate follows the same temperature dependence, determined by magnon scattering mechanisms, observed in the bulk by 153Eu NMR, but above 40 K, the signal is wiped out. We also find that 8Li+ stopped in material adjacent to the magnetic layer exhibits spin relaxation related to the critical slowing of the Eu spins. A particularly strong relaxation in the Au overlayer suggests an unusual strong nonlocal coupling mechanism to 8Li in the metal.
10.1103/PhysRevB.92.064409
Title
Nanoscale β-nuclear magnetic resonance depth imaging of topological insulators
Author
D. Koumoulis, G. D. Morris, L. He, X. Kou, D. King, D. Wang, M. D. Hossain, K. L. Wang, G. A. Fiete, M. G. Kanatzidis, L.-S. Bouchard
Journal
Proceedings of the National Academy of Sciences of the United States of America
Volume
112
Issue
28
Pages
E3645-E3650
Year
2015
Abstract
Considerable evidence suggests that variations in the properties of topological insulators (TIs) at the nanoscale and at interfaces can strongly affect the physics of topological materials. Therefore, a detailed understanding of surface states and interface coupling is crucial to the search for and applications of new topological phases of matter. Currently, no methods can provide depth profiling near surfaces or at interfaces of topologically inequivalent materials. Such a method could advance the study of interactions. Herein, we present a noninvasive depth-profiling technique based on β-detected NMR (β-NMR) spectroscopy of radioactive 8Li+ ions that can provide "one-dimensional imaging" in films of fixed thickness and generates nanoscale views of the electronic wavefunctions and magnetic order at topological surfaces and interfaces. By mapping the 8Li nuclear resonance near the surface and 10-nm deep into the bulk of pure and Cr-doped bismuth antimony telluride films, we provide signatures related to the TI properties and their topological nontrivial characteristics that affect the electron-nuclear hyperfine field, the metallic shift, and magnetic order. These nanoscale variations in β-NMR parameters reflect the unconventional properties of the topological materials under study, and understanding the role of heterogeneities is expected to lead to the discovery of novel phenomena involving quantum materials.
10.1073/pnas.1502330112
arXiv:1506.0894 [cond-mat.mtrl-sci]
Title
Spin fluctuations in the exotic metallic state of Sr2RuO4 studied with β-NMR
Author
D. L. Cortie, T. Buck, M. H. Dehn, R. F. Kiefl, C. D. P. Levy, R. M. L. McFadden, G. D. Morris, M. R. Pearson, Z. Salman, Y. Maeno, W. A. MacFarlane
Journal
Physical Review B
Volume
91
Issue
24
Pages
241113(R)
Year
2015
Abstract
A β-NMR study was performed on a Sr2RuO4 crystal in the metallic state using a beam of spin-polarized 8Li+ implanted at a mean depth of 90 nm. The 8Li+ spin-lattice relaxation rate is strongly influenced by the onset of incommensurate spin fluctuations. The nuclear relaxation rate can be explained using previously published bulk 17O NMR and inelastic neutron spectroscopy measurements of the dynamic magnetic susceptibility to model the hyperfine coupling. A well-resolved quadrupolar-split NMR for 8Li+ implies a static stopping position in an interstitial site. The 8Li+ Knight shift is highly sensitive to the anisotropic static susceptibility.
10.1103/PhysRevB.91.241113
Title
Enhanced high-frequency molecular dynamics in the near-surface region of polystyrene thin films observed with β-NMR
Author
I. McKenzie, C. R. Daley, R. F. Kiefl, C. D. P. Levy, W. A. MacFarlane, G. D. Morris, M. R. Pearson, D. Wang, J. A. Forrest
Journal
Soft Matter
Volume
11
Issue
9
Pages
1755-1761
Year
2015
Abstract
β-detected nuclear spin relaxation of 8Li+ has been used to probe the depth dependence of molecular dynamics in high- and low-molecular-weight deuterated polystyrene. The average nuclear spin-lattice relaxation rate, 1/T1avg, is a measure of the spectral density of the polymer motion at the Larmor frequency (41 MHz at 6.55 T). In both samples, 1/T1avg is depth independent below ~200 K but above this temperature it decreases approximately exponentially with distance from the free surface, returning to bulk behavior for depths greater than ~10 nm. This is direct evidence for a region near the free surface with enhanced molecular dynamics compared with the bulk. The effective thickness of the surface region increases with increasing temperature and is finite even above the glass transition. These results present challenges for the current understanding of dynamics near the surface of polymer glasses.
10.1039/C4SM02245A
2014
Title
β-detected NMR of 8Li+ in Bi, Sb, and the topological insulator Bi0.9Sb0.1
Author
W. A. MacFarlane, C. B. L. Tschense, T. Buck, K. H. Chow, D. L. Cortie, A. N. Hariwal, R. F. Kiefl, D. Koumoulis, C. D. P. Levy, I. McKenzie, F. H. McGee, G. D. Morris, M. R. Pearson, Q. Song, D. Wang, Y. S. Hor, R. J. Cava
Journal
Physical Review B
Volume
90
Issue
21
Pages
214422
Year
2014
Abstract
We report the NMR Knight shift and spin-lattice relaxation of 8Li+ implanted ~100 nm into single crystals of semimetallic Sb, Bi, and topologically insulating Bi0.9Sb0.1. We find small negative shifts (of order 100 ppm) in all three. In the insulator, the shift is nearly temperature independent, while in Bi and Sb it becomes more negative at low temperature without following the bulk susceptibility, suggesting two distinct temperature dependent contributions, possibly from the orbital and spin response. However, a simple model is unable to account for the observed shift. The spin-lattice relaxation differs in both scale and temperature dependence in all three. It is Korringa-like in Bi and remarkably is fastest in the insulating alloy and slowest in Sb with the highest bulk carrier density. These surprising results call for detailed calculations, but phenomenologically demonstrate that β-detected NMR of implanted 8Li+ is sensitive to the magnetic response of low-density carriers. The prospects for depth-resolved studies of conventional and topological surface states at lower implantation energies are good.
10.1103/PhysRevB.90.214422
Title
β-NMR measurements of lithium ion transport in thin films of pure and lithium-salt-doped poly(ethylene oxide)
Author
I. McKenzie, M. Harada, R. F. Kiefl, C. D. P. Levy, W. A. MacFarlane, G. D. Morris, S.-I. Ogata, M. R. Pearson, J. Sugiyama
Journal
Journal of the American Chemical Society
Volume
136
Issue
2
Pages
7833-7836
Year
2014
Abstract
β-Detected nuclear spin relaxation of 8Li+ has been used to study the microscopic diffusion of lithium ions in thin films of poly(ethylene oxide) (PEO), where the implanted lithium ions are present in extremely low concentration, and PEO with 30 wt % LiCF3SO3 over a wide range of temperatures both above and below the glass transition temperature. Recent measurements by Do et al. [Physical Review Letters 2013, 111, 018301] found that the temperature dependence of the Li+ conductivity was identical to that of the dielectric α relaxation and was well described by the Vogel-Fulcher-Tammann relation, implying the α relaxation dominates the Li+ transport process. In contrast, we find the hopping of Li+ in both samples in the high temperature viscoelastic phase follows an Arrhenius law and depends significantly on the salt content. We propose that the hopping of Li+ between cages involves motion of the polymer but that it is only for long-range diffusion where the α relaxation plays an important role.
10.1021/ja503066a
Title
High precision measurement of the 11Li and 9Li quadrupole moment ratio using zero field β-NQR
Author
A. Voss, M. R. Pearson, F. Buchinger, J. E. Crawford, R. F. Kiefl, C. D. P. Levy, W. A. MacFarlane, E. Mané, G. D. Morris, O. T. J. Shelbaya, Q. Song, D. Wang
Journal
Journal of Physics G: Nuclear and Particle Physics
Volume
14
Issue
1
Pages
015104
Year
2014
Abstract
The ratio of electric quadrupole moments of 11Li and 9Li was measured using the zero-field β-detected nuclear quadrupole resonance technique at TRIUMF-ISAC. The precision on the ratio Q11/Q9 = 1.0775(12) was improved by more than one order of magnitude and an absolute value for the quadrupole moment of 11Li was inferred. Systematic effects, as argued here, are not expected to contribute to the ratio on this scale. The zero-field spin-lattice relaxation time for 8Li implanted within SrTiO3 at 295 K in zero-field was found to be T1 = 1.73(2) s. A comparison of the quadrupole moments of 9,11Li and their ratio is made with the latest models, however, no conclusion may yet be drawn owing to the size of the theoretical uncertainties.
10.1088/0954-3899/41/1/015104
2013
Title
Finite-size effects in the nuclear magnetic resonance of epitaxial palladium thin films
Author
W. A. MacFarlane, T. J. Parolin, T. I. Larkin, G. Richter, K. H. Chow, M. D. Hossain, R. F. Kiefl, C. D. P. Levy, G. D. Morris, O. Ofer, M. R. Pearson, H. Saadaoui, Q. Song, D. Wang
Journal
Physical Review B
Volume
88
Issue
14
Pages
144424
Year
2013
Abstract
We have measured the NMR of 8Li+ implanted in a set of thin epitaxial films of Pd. We find a large, negative, strongly temperature-dependent Knight shift K consistent with previous measurements on polycrystalline films. The temperature dependence of the shift exhibits a characteristic deviation from the susceptibility χ(T). In particular, at low temperature, K(T) continues to follow a simple Curie-Weiss dependence. This result provides important insight into the origin of the low-temperature behavior of χ(T) in strongly paramagnetic metals. In addition, we find the room temperature shift depends on film thickness, with changes on the order of 20 % between films 100 nm and 30 nm thick. We also observe a surface-related resonance in both Au-capped and uncapped films with a small positive shift. These features bear a striking similarity to the Pt NMR line shapes in much smaller Pt particles. However, they seem to originate, not from adsorbed species, but rather in confinement effects on the highly exhange-enhanced Pd d band.
10.1103/PhysRevB.88.144424
2012
Title
Nature of weak magnetism in SrTiO3/LaAlO3 Multilayers
Author
Z. Salman, O. Ofer, M. Radovic, H. Hao, M. Ben Shalom, K. H. Chow, Y. Dagan, M. D. Hossain, C. D. P. Levy, W. A. MacFarlane, G. M. Morris, L. Patthey, M. R. Pearson, H. Saadaoui, T. Schmitt, D. Wang, R. F. Kiefl
Journal
Physical Review Letters
Volume
109
Issue
25
Pages
257207
Year
2012
Abstract
We report the observation of weak magnetism in superlattices of LaAlO3/SrTiO3 using β-detected nuclear magnetic resonance. The spin lattice relaxation rate of 8Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO3 exhibits a strong peak near ~35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO3/SrTiO3 interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of ~4-6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (~0.002 μB) in the two samples with a larger LaAlO3 spacer thickness.
10.1103/PhysRevLett.109.257207
arXiv:1211.4961 [cond-mat.mtrl-sci]
Title
β-NMR study of isolated 8Li+ in the enhanced paramagnet platinum
Author
O. Ofer, K. H. Chow, I. Fan, M. Egilmez, T. J. Parolin, M. D. Hossain, J. Jung, Z. Salman, R. F. Kiefl, C. D. P. Levy, G. D. Morris, M. R. Pearson, H. Saadaoui, Q. Song, D. Wang, W. A. MacFarlane
Journal
Physical Review B
Volume
86
Issue
6
Pages
064419
Year
2012
Abstract
We report β-detected nuclear magnetic resonance (β-NMR) measurements of 8Li+ implanted into high purity Pt. The frequency of the 8Li β-NMR resonance and the spin-lattice relaxation rates 1/T1 were measured at temperatures ranging from 3 to 300 K. Remarkably, both the spin-lattice relaxation rate and the Knight shift K depend linearly on temperature T although the bulk susceptibility does not. K is found to scale with the Curie-Weiss dependence of the Pt susceptibility extrapolated to low temperatures. This is attributed to a defect response of the enhanced paramagnetism of Pt, i.e., the presence of the interstitial Li+ locally relieves the tendency for the Curie-Weiss susceptibility to saturate at low T. We propose that the low temperature saturation in χ of Pt may be related to an interband coupling between the s and d bands that is disrupted locally by the presence of the Li+.
10.1103/PhysRevB.86.064419
arXiv:1208.3873 [cond-mat.str-el]
Title
Slow order-parameter fluctuations in superconducting Pb and Ag/Nb films observed using β-detected nuclear magnetic resonance
Author
E. Morenzoni, H. Saadaoui, D. Wang, M. Horisberger, E. C. Kirk, W. A. MacFarlane, G. D. Morris, K. H. Chow, M. D. Hossain, C. P. Levy, T. J. Parolin, M. R. Pearson, Q. Song, R. F. Kiefl
Journal
Physical Review B
Volume
85
Issue
22
Pages
220501(R)
Year
2012
Abstract
We report β-NMR investigations of polarized 8Li implanted in thin Pb and Ag/Nb films. At the critical superconducting temperature, we observe a singular peak in the spin relaxation rate in small longitudinal magnetic fields, which is attributed to unexpected slow fluctuations in the superconducting order parameter. The peak is several orders of magnitude larger than the prediction based on the enhancement of the dynamic electron spin susceptibility by superconducting fluctuations. The observed peak in 1/T1 is rapidly suppressed in a small magnetic field, indicating that it is due to remarkably slow diamagnetic fluctuations which are undetectable with conventional NMR.
10.1103/PhysRevB.85.220501
arXiv:1109.4508 [cond-mat.supr-con]
Title
Detection and decoherence of level-crossing resonances of 8Li in Cu
Author
K. H. Chow, A. I. Mansour, I. Fan, R. F. Kiefl, G. D. Morris, Z. Salman, T. Dunlop, W. A. MacFarlane, H. Saadaoui, O. Mosendz, B. Kardasz, B. Heinrich, J. Jung, C. D. P. Levy, M. R. Pearson, T. J. Parolin, D. Wang, M. D. Hossain, Q. Song, M. Smadella
Journal
Physical Review B
Volume
85
Issue
9
Pages
092103
Year
2012
Abstract
Level-crossing resonances are observed for spin-polarized 8Li in copper at 200 K. The positions of the resonances as a function of magnetic field and crystal orientation are a precise measure of the induced quadrupolar interaction on the nearest-neighbor Cu spins and provide unambiguous evidence that 8Li occupies a substitutional site. The resonances are detected as enhancements in the 8Li spin relaxation rate and are much broader than predicted from a static spin Hamiltonian. A strong collision model is used to extract a decoherence time as a result of the dipolar coupling of the 8Li-Cu subsystem to the surrounding nuclear spin bath.
10.1103/PhysRevB.85.092103
2011
Title
β-detected NMR of Li in Ga1-xMnxAs
Author
Q. Song, K. H. Chow, Z. Salman, H. Saadaoui, M. D. Hossain, R. F. Kiefl, G. D. Morris, C. D. P. Levy, M. R. Pearson, T. J. Parolin, I. Fan, T. A. Keeler, M. Smadella, D. Wang, K. M. Yu, X. Liu, J. K. Furdyna, W. A. MacFarlane
Journal
Physical Review B
Volume
84
Issue
5
Pages
054414
Year
2011
Abstract
The magnetic properties of a 180-nm-thick epitaxial film of the dilute magnetic semiconductor Ga1-xMnx with x = 0.054 are investigated using beta-detected NMR of low-energy implanted 8Li+. There is a broad distribution of local magnetic fields in the Ga1-xMnx layer, reflecting the magnetic inhomogeneity of the system. The resonance (representing the local magnetic field distribution) is followed as a function of temperature through the ferromagnetic transition. The average hyperfine field at the 8Li nucleus is measured to be positive and on the order of 150 G at low temperature, implying a negative hyperfine coupling of the 8Li to the delocalized holes and suggesting that the holes are better described by an Mn-derived impurity band. The spin-lattice relaxation of 8Li shows a remarkably weak feature at the phase transition and no Korringa behavior despite metallic conductivity. No evidence is found of the microscopic magnetic phase separation that has been suggested by some low-energy muon spin-rotation measurements.
10.1103/PhysRevB.84.054414
Title
Depth dependence of the structural phase transition of SrTiO3 studied with β-NMR and grazing incidence x-ray diffraction
Author
Z. Salman, M. Smadella, W. A. MacFarlane, B. D. Patterson, P. R. Willmott, K. H. Chow, M. D. Hossain, H. Saadaoui, D. Wang, R. F. Kiefl
Journal
Physical Review B
Volume
83
Issue
22
Pages
224112
Year
2011
Abstract
We present an investigation of the near-surface tetragonal phase transition in SrTiO3, using the complementary techniques of beta-detected nuclear magnetic resonance and grazing-incidence X-ray diffraction. The results show a clear depth dependence of the phase transition on scales of a few microns. The measurements support a model in which there are tetragonal domains forming in the sample at temperatures much higher than the bulk phase transition temperature. Moreover, we find that these domains tend to form at higher temperatures preferentially near the free surface of the crystal. The details of the tetragonal domain formation and their depth/lateral dependencies are discussed.
10.1103/PhysRevB.83.224112
arXiv:1105.1032 [cond-mat.mtrl-sci]
Title
Nuclear electric quadrupole moment of 9Li using zero-field β-detected NQR
Author
A. Voss, M. R. Pearson, J. Billowes, F. Buchinger, K. H. Chow, J. E. Crawford, M. D. Hossein, R. F. Kiefl, C. D. P. Levy, W. A. MacFarlane, E. Mané, G. D. Morris, T. J. Parolin, H. Saadaoui, Z. Salman, M. Smadella, Q. Song, D. Wang
Journal
Journal of Physics G: Nuclear and Particle Physics
Volume
38
Issue
7
Pages
075102
Year
2011
Abstract
A β-detected nuclear quadrupole resonance (NQR) spectrometer becomes a powerful tool to study changes in nuclear ground-state properties along isotopic chains when coupled to a laser excitation beamline to polarize the nuclei of interest. Recently, the β-NQR technique in a zero magnetic field has been applied for the first time to measure the ratio of static nuclear quadrupole moments of 8,9Li, Q9/Q8 = 0.96675(9) denoted by Q8 for 8Li and Q9 for 9Li, respectively. This shows agreement with present literature values but with significantly improved precision. Based on the literature, the quadrupole moment for 8Li has been re-evaluated to be |Q8| = 32.6(5) mb. From this, the quadrupole moment for 9Li is calculated as |Q9| = 31.5(5) mb with the error being dominated by the error of Q8.
10.1088/0954-3899/38/7/075102
Title
Search for broken time-reversal symmetry near the surface of superconducting YBa2Cu3O7-δ films using β-detected nuclear magnetic resonance
Author
H. Saadaoui, G. D. Morris, Z. Salman, Q. Song, K. H. Chow, M. D. Hossain, C. D. P. Levy, T. J. Parolin, M. R. Pearson, M. Smadella, D. Wang, L. H. Greene, P. J. Hentges, R. F. Kiefl, W. A. MacFarlane
Journal
Physical Review B
Volume
83
Issue
5
Pages
054504
Year
2011
Abstract
Weak spontaneous magnetic fields are observed near the surface of YBa2Cu3O7-δ films using β-detected nuclear magnetic resonance. Below Tc, the magnetic field distribution in a silver film evaporated onto the superconductor shows additional line broadening, indicating the appearance of small disordered magnetic fields. The line broadening increases linearly with a weak external magnetic field applied parallel to the surface, and is depth independent up to 45 nm from the Ag/YBa2Cu3O7-δ interface. The magnitude of the line broadening extrapolated to zero applied field is less than 0.2 G, and is close to nuclear dipolar broadening in the Ag. This indicates that any fields due to broken time-reversal symmetry are less than 0.2 G.
10.1103/PhysRevB.83.054504
arXiv:1101.0930 [cond-mat.supr-con]
2010
Title
Nuclear polarization of short-lived Na isotopes maintained in single crystals for β-NMR spectroscopy
Author
K. Minamisono, K. Matsuta, T. Minamisono, C. D. P. Levy, T. Nagatomo, M. Ogura, T. Sumikama, J. A. Behr, K. P. Jackson, M. Mihara, M. Fukuda
Journal
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Volume
616
Issue
1
Pages
45-54
Year
2010
Abstract
A compact β-ray detecting nuclear magnetic/quadrupole resonance system with a permanent magnet was developed at ISAC/TRIUMF to measure ground-state electromagnetic moments of short-lived nuclei. Polarized Na beams produced using the collinear optical-pumping technique were used to demonstrate the properties of the system. The degree of nuclear polarization and the spin–lattice relaxation times of the 20,21,26,27,28Na isotopes in NaF, TiO2, LiNbO3, MgF2, ZnO, Pt, and Mg single crystals at room temperature are reported. The electric-quadrupole coupling constants of 20,21Na in TiO2, ZnO and Mg, and that of 27Na in ZnO are also reported. The quadrupole moments of 20,21Na were extracted from the electric-quadrupole coupling constants in ZnO, using the known quadrupole moment of 27Na.
10.1016/j.nima.2010.02.101
2009
Title
Vortex lattice disorder in YBa2Cu3O7-δ probed using β-NMR
Author
H. Saadaoui, W. A. MacFarlane, Z. Salman, G. D. Morris, Q. Song, K. H. Chow, M. D. Hossain, C. D. P. Levy, A. I. Mansour, T. J. Parolin, M. R. Pearson, M. Smadella, D. Wang, R. F. Kiefl
Journal
Physical Review B
Volume
80
Issue
22
Pages
224503
Year
2009
Abstract
β-detected NMR (β-NMR) has been used to study vortex lattice disorder near the surface of the high-TC superconductor YBa2Cu3O7-δ (YBCO). The magnetic-field distribution from the vortex lattice was detected by implanting a low-energy beam of highly polarized 8Li+ into a thin overlayer of silver on optimally doped, twinned, and detwinned YBCO samples. The resonance in Ag broadens significantly below the transition temperature TC as expected from the emerging field lines of the vortex lattice in YBCO. However, the lineshape is more symmetric and the dependence on the applied magnetic field is much weaker than expected from an ideal vortex lattice, indicating that the vortex density varies across the face of the sample, likely due to pinning at twin boundaries. At low temperatures the broadening from such disorder does not scale with the superfluid density.
10.1103/PhysRevB.80.224503
arXiv:1003.1166 [cond-mat.supr-con]
Title
Nuclear magnetic resonance study of Li implanted in a thin film of niobium
Author
T. J. Parolin, J. Shi, Z. Salman, K. H. Chow, P. Dosanjh, H. Saadaoui, Q. Song, M. D. Hossain, R. F. Kiefl, C. D. P. Levy, M. R. Pearson, W. A. MacFarlane
Journal
Physical Review B
Volume
80
Issue
17
Pages
174109
Year
2009
Abstract
We report results of beta-detected NMR of 8Li+ implanted in Nb at high magnetic field. We identify two distinct sites for 8Li in the body-centered lattice. At low temperature, the site is characterized by a well-defined quadrupolar splitting. At about 50 K this site becomes unstable. Close to room temperature, Li occupies the cubic substitutional site. Spin-lattice relaxation measurements are consistent with a site-dependent coupling to the Nb conduction electrons and suggest that the site change proceeds in two steps. We report Knight shifts for the two well-defined sites and perform a Korringa analysis.
10.1103/PhysRevB.80.174109
Title
Low-field cross spin relaxation of 8Li in superconducting NbSe2
Author
M. D. Hossain, Z. Salman, D. Wang, K. H. Chow, S. Kreitzman, T. A. Keeler, C. D. P. Levy, W. A. MacFarlane, R. I. Miller, G. D. Morris, T. J. Parolin, M. Pearson, H. Saadaoui, R. F. Kiefl
Journal
Physical Review B
Volume
79
Issue
14
Pages
144518
Year
2009
Abstract
A low energy beam of spin polarized 8Li has been used to investigate nuclear spin relaxation in the multiband superconductor NbSe2. In low magnetic fields there is significant cross relaxation between the 8Li and the host 93Nb spins, which is driven by low frequency fluctuations in the nuclear magnetic dipolar interaction. The rate of cross relaxation is strongly field dependent and thus the 1/T1 spin relaxation rate of the 8Li is a sensitive monitor of the static local magnetic field B just below the surface. This in turn is used to determine the absolute value of the magnetic penetration depth λ in the Meissner state. The temperature variations in 1/T1 and λ are consistent with a wide distribution of superconducting gaps expected for a multiband superconductor.
10.1103/PhysRevB.79.144518
Title
Quadrupole moments of neutron-deficient 20,21Na
Author
K. Minamisono, K. Matsuta, T. Minamisono, C. D. P. Levy, T. Nagatomo, M. Ogura, T. Sumikama, J. A. Behr, K. P. Jackson, M. Mihara, M. Fukuda
Journal
Physics Letters B
Volume
672
Issue
2
Pages
120-125
Year
2009
Abstract
The electric-quadrupole coupling constant of the ground states of the proton drip line nucleus 20Na (Iπ = 2+, T1/2 = 447.9 ms) and the neutron-deficient nucleus 21Na (Iπ = 3/2+, T1/2 = 22.49 s) in a hexagonal ZnO single crystal were precisely measured to be |eqQ/h| = 690 ± 12 kHz and 939 ± 14 kHz, respectively, using the multi-frequency β-ray detecting nuclear magnetic resonance technique under presence of an electric-quadrupole interaction. An electric-quadrupole coupling constant of 27Na in the ZnO crystal was also measured to be |eqQ/h| = 48.4 ± 3.8 kHz. The electric-quadrupole moments were extracted as |Q(20Na)| = 10.3 ± 0.8 e fm2 and |Q(21Na)| = 14.0 ± 1.1 e fm2, using the electric-coupling constant of 27Na and the known quadrupole moment of this nucleus as references. The present results are well explained by shell-model calculations in the full sd-shell model space.
10.1016/j.physletb.2009.01.006
2008
Title
High resolution β-NMR study of 8Li+ implanted in gold
Author
T. J. Parolin, Z. Salman, K. H. Chow, Q. Song, J. Valiani, H. Saadaoui, A. O’Halloran, M. D. Hossain, T. A. Keeler, R. F. Kiefl, S. R. Kreitzman, C. D. P. Levy, R. I. Miller, G. D. Morris, M. R. Pearson, M. Smadella, D. Wang, M. Xu, W. A. MacFarlane
Journal
Physical Review B
Volume
77
Issue
21
Pages
214107
Year
2008
Abstract
We report the behavior of low energy 8Li+ implanted into gold as revealed by beta-detected NMR. At an external magnetic field of 3 T, two narrow resonances are observed, which are attributed to Li in the octahedral interstitial and the substitutional lattice sites. The Knight shifts for these two resonances are found to be temperature independent with values of +141(4) and +73(5) ppm, respectively. The spin-lattice relaxation rate in high magnetic fields at 290 K is slow, consistent with the Korringa relation; however, the rate increases dramatically for magnetic fields below about 2 mT. We attribute this to interaction of the 8Li spin with the host lattice nuclear spins.
10.1103/PhysRevB.77.214107
Title
Hyperfine fields in an Ag/Fe multilayer film investigated with 8Li β-detected NMR
Author
T. A. Keeler, Z. Salman, K. H. Chow, B. Heinrich, M. D. Hossian, B. Kardasz, R. F. Kiefl, S. R. Kreitzman, C. D. P. Levy, W. A. MacFarlane, O. Mosendz, T. J. Parolin, M. R. Pearson, D. Wang
Journal
Physical Review B
Volume
77
Issue
14
Pages
144429
Year
2008
Abstract
Low-energy β-detected nuclear magnetic resonance was used to investigate the spatial dependence of the hyperfine magnetic fields induced by Fe in the nonmagnetic Ag of an Au(40 Å)/Ag(200 Å)/Fe(140 Å) (001) magnetic multilayer grown on GaAs. The resonance line shape in the Ag layer shows dramatic broadening compared to that of intrinsic Ag. This broadening is attributed to large magnetic fields induced in this layer by the magnetic Fe layer. We find that the induced hyperfine field in the Ag follows a power law decay away from the Ag/Fe interface with power −1.93(8), and a field extrapolated to 0.23(5) T at the interface.
10.1103/PhysRevB.77.144429
arXiv:0803.3874 [cond-mat.str-el]
Title
Proximal magnetometry in thin films using βNMR
Author
M. Xu, M. D. Hossain, H. Saadaoui, T. J. Parolin, K. H. Chow, T. A. Keeler, R. F. Kiefl, G. D. Morris, Z. Salman, Q. Song, D. Wang, W. A. MacFarlane
Journal
Journal of Magnetic Resonance
Volume
191
Issue
1
Pages
47-55
Year
2008
Abstract
Low energy ion implantation of hyperpolarized radioactive magnetic resonance probes allows the NMR study of thin film heterostructures by enabling depth-resolved measurements on a nanometer lengthscale. By stopping the probe ions in a layer adjacent to a layer of interest, it is possible to study magnetic fields proximally. Here we show that, in the simplest case of a uniformly magnetized layer, this yields an unperturbed in situ frequency reference. We also discuss demagnetization contributions to measured shifts for this case. With a simple illustrative calculation, we show how a nonuniformly magnetized layer causes a strongly depth-dependent line broadening in an adjacent layer. We then give some experimental examples of resonance line broadening in heterostructures.
10.1016/j.jmr.2007.11.022
2007
Title
Local magnetic properties of a monolayer of Mn12 single molecule magnets
Author
Z. Salman, K. H. Chow, R. I. Miller, A. Morello, T. J. Parolin, M. D. Hossain, T. A. Keeler, C. D. P. Levy, W. A. MacFarlane, G. D. Morris, H. Saadaoui, D. Wang, R. Sessoli, G. G. Condorelli, R. F. Kiefl
Journal
Nano Letters
Volume
7
Issue
6
Pages
1551
Year
2007
Abstract
The magnetic properties of a monolayer of Mn12 single molecule magnets grafted onto a silicon (Si) substrate have been investigated using depth-controlled β-detected nuclear magnetic resonance. A low-energy beam of spin-polarized radioactive 8Li was used to probe the local static magnetic field distribution near the Mn12 monolayer in the Si substrate. The resonance line width varies strongly as a function of implantation depth as a result of the magnetic dipolar fields generated by the Mn12 electronic magnetic moments. The temperature dependence of the line width indicates that the magnetic properties of the Mn12 moments in this low-dimensional configuration differ from bulk Mn12.
10.1021/nl070366a
arXiv:0804.4794 [cond-mat.mes-hall]
Title
Magnetic-field effects on the size of vortices below the surface of NbSe2 detected using low energy β-NMR
Author
Z. Salman, D. Wang, K. H. Chow, M. D. Hossain, S. R. Kreitzman, T. A. Keeler, C. D. P. Levy, W. A. MacFarlane, R. I. Miller, G. D. Morris, T. J. Parolin, H. Saadaoui, M. Smadella, R. F. Kiefl
Journal
Physical Review Letters
Volume
98
Issue
16
Pages
167001
Year
2007
Abstract
A low energy radioactive beam of polarized 8Li has been used to observe the vortex lattice near the surface of superconducting NbSe2. The inhomogeneous magnetic-field distribution associated with the vortex lattice was measured using depth-resolved β-detected NMR. Below Tc, one observes the characteristic line shape for a triangular vortex lattice which depends on the magnetic penetration depth and vortex core radius. The size of the vortex core varies strongly with the magnetic field. In particular, in a low field of 10.8 mT, the core radius is much larger than the coherence length. The possible origin of these giant vortices is discussed.
10.1103/PhysRevLett.98.167001
arXiv:cond-mat/0703174 [cond-mat.str-el]
Title
β-NMR of isolated 8Li+ implanted into a thin copper film
Author
Z. Salman, A. I. Mansour, K. H. Chow, M. Beaudoin, I. Fan, J. Jung, T. A. Keeler, R. F. Kiefl, C. D. P. Levy, R. C. Ma, G. D. Morris, T. J. Parolin, D. Wang, W. A. MacFarlane
Journal
Physical Review B
Volume
75
Issue
7
Pages
073405
Year
2007
Abstract
Depth-controlled β-NMR was used to study highly spin-polarized 8Li+ in a Cu film of thickness 100 nm deposited onto a MgO substrate. The positive Knight shifts and spin relaxation data show that 8Li+ occupies two sites at low temperatures, assigned to be the substitutional (S) and octahedral (O) interstitial sites. Between 50 and 150 K, there is a site change from O to S. The temperature dependence of the Knight shifts and spin-lattice relaxation rates at high temperatures, i.e., when all the Li are in the S site, is consistent with the Korringa law for a simple metal.
10.1103/PhysRevB.75.073405
arXiv:cond-mat/0701002 [cond-mat.str-el]
Title
β-NMR of isolated lithium in nearly ferromagnetic palladium
Author
T. J. Parolin, Z. Salman, J. Chakhalian, Q. Song, K. H. Chow, M. D. Hossain, T. A. Keeler, R. F. Kiefl, S. R. Kreitzman, C. D. P. Levy, R. I. Miller, G. D. Morris, M. R. Pearson, H. Saadaoui, D. Wang, W. A. MacFarlane
Journal
Physical Review Letters
Volume
98
Issue
4
Pages
047601
Year
2007
Abstract
The temperature dependence of the frequency shift and spin-lattice relaxation rate of isolated, nonmagnetic 8Li impurities implanted in a nearly ferromagnetic host (Pd) are measured by means of β-detected nuclear magnetic resonance (β-NMR). The shift is negative, very large, and increases monotonically with decreasing T in proportion to the bulk susceptibility of Pd for T > T* ≈ 100 K. Below T*, an additional shift occurs which we attribute to the response of Pd to the defect. The relaxation rate is much slower than expected for the large shift and is linear with T below T*, showing no sign of additional relaxation mechanisms associated with the defect.
10.1103/PhysRevLett.98.047601
arXiv:cond-mat/0701394 [cond-mat.mtrl-sci]
2006
Title
Near-surface structural phase transition of SrTiO3 studied with zero-field β-detected nuclear spin relaxation and resonance
Author
Z. Salman, R. F. Kiefl, K. H. Chow, M. D. Hossain, T. A. Keeler, S. R. Kreitzman, C. D. P. Levy, R. I. Miller, T. J. Parolin, M. R. Pearson, H. Saadaoui, J. D. Schultz, M. Smadella, D. Wang, W. A. MacFarlane
Journal
Physical Review Letters
Volume
96
Issue
14
Pages
147601
Year
2006
Abstract
We demonstrate that zero-field β-detected nuclear quadrupole resonance and spin relaxation of low energy 8Li can be used as a sensitive local probe of structural phase transitions near a surface. We find that the transition near the surface of a SrTiO3 single crystal occurs at Tc ~ 150 K, i.e., ~45 K higher than Tcbulk, and that the tetragonal domains formed below Tc are randomly oriented.
10.1103/PhysRevLett.96.147601
arXiv:cond-mat/0511526 [cond-mat.stat-mech]
2004
Title
Depth-controlled β-NMR of 8Li in a thin silver film
Author
G. D. Morris, W. A. MacFarlane, K. H. Chow, Z. Salman, D. J. Arseneau, S. Daviel, A. Hatakeyama, S. R. Kreitzman, C. D. P. Levy, R. Poutissou, R. H. Heffner, J. E. Elenewski, L. H. Greene, R. F. Kiefl
Journal
Physical Review Letters
Volume
93
Issue
15
Pages
157601
Year
2004
Abstract
Depth-controlled β-NMR can be used to probe the magnetic properties of thin films and interfaces on a nanometer length scale. A 30 keV beam of highly spin-polarized 8Li+ ions was slowed down and implanted into a 50 nm film of Ag deposited on a SrTiO3 substrate. A novel high field β-NMR spectrometer was used to observe two well resolved resonances which are attributed to Li occupying substitutional and octahedral interstitial sites in the Ag lattice. The temperature dependence of the Knight shifts and spin relaxation rates are consistent with the Korringa law for a simple metal, implying that the NMR of implanted 8Li reflects the spin suspectibility of bulk metallic silver.
10.1103/PhysRevLett.93.157601
Title
β-detected nuclear quadrupole resonance with a low-energy beam of 8Li+
Author
Z. Salman, E. P. Reynard, W. A. MacFarlane, K. H. Chow, J. Chakhalian, S. R. Kreitzman, S. Daviel, C. D. P. Levy, R. Poutissou, R. F. Kiefl
Journal
Physical Review B
Volume
70
Issue
10
Pages
104404
Year
2004
Abstract
A nuclear quadrupole resonance (NQR) spectrum of 8Li has been observed in a single crystal of SrTiO3 using a beam of low-energy highly polarized radioactive 8Li+. The resonances were detected by monitoring the β-decay anisotropy as a function of a small audio frequency magnetic field. These results demonstrate that low energy nuclear spin polarized 8Li can be used as a sensitive probe of the local magnetic and electronic environment in nanostructures and ultrathin films in zero static applied magnetic field.
10.1103/PhysRevB.70.104404

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