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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
[show abstract]
[hide abstract]
ABSTRACT: We report the observation of weak magnetism in superlattices of LaAlO_{3}/SrTiO_{3} using β-detected nuclear magnetic resonance. The spin lattice relaxation rate of ^{8}Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO_{3} 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 LaAlO_{3}/SrTiO_{3} 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 (∼0.002μ_{B}) in the two samples with a larger LaAlO_{3} spacer thickness.
Physical Review Letters 12/2012; 109(25):257207. · 7.37 Impact Factor
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Z. Salman,
O. Ofer,
M. Radovic,
H. Hao,
K. H. Chow,
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
[show abstract]
[hide abstract]
ABSTRACT: We report the observation of weak magnetism in superlattices of LaAlO3/SrTiO3
using beta-detected nuclear magnetic resonance. The spin lattice relaxation
rate of 8 Li 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 muB) in the two samples with a larger
LaAlO3 spacer thickness.
11/2012;
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Oren 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
[show abstract]
[hide abstract]
ABSTRACT: We report {\beta} detected nuclear magnetic resonance ({\beta}NMR)
measurements of 8Li+ implanted into high purity Pt. The frequency of the 8Li
{\beta}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 \c{hi} 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+.
08/2012;
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E. Mané,
J. A. Behr,
J. Billowes,
T. Brunner,
M. Brodeur,
F. Buchinger,
J. E. Crawford,
J. Dilling,
S. Ettenauer, C. D. P. Levy,
A. Voss,
M. R. Pearson
[show abstract]
[hide abstract]
ABSTRACT: Collinear laser spectroscopy with reverse-extracted cooled bunched beams was performed at TRIUMF with radioactive ion beams.
Surface-ionized 78,78mRb ions were injected into TITAN’s cooler-buncher, and reverse-extracted to the laser beam line. There they were neutralised
and excited with a counter-propagating laser beam. The fluorescence signal from the D
2 line was recorded with a photomultiplier tube. The cooler provided typically 50 ion bunches per second, with each bunch containing
approximately 105 ions, temporally distributed with a 1.6 μs width. A hardware gate was set on the signal, suppressing the background by four orders of magnitude.
KeywordsLaser spectroscopy–Hyperfine Structure–Cooling and bunching
Hyperfine Interactions 04/2012; 199(1):357-363. · 0.21 Impact Factor
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C. D. P. Levy,
M. R. Pearson,
G. D. Morris,
K. H. Chow,
M. D. Hossain,
R. F. Kiefl,
R. Labbé,
J. Lassen,
W. A. MacFarlane,
T. J. Parolin,
H. Saadaoui,
M. Smadella,
Q. Song,
D. Wang
[show abstract]
[hide abstract]
ABSTRACT: The low-energy collinear laser beam line at ISAC routinely produces highly nuclear-spin polarized beams of 8Li + for depth-controlled studies of thin films and near-surface phenomena. It also is used for nuclear structure and fundamental
symmetry studies requiring other beams of polarized lithium and sodium isotopes. Further development of polarized 20F and 11Be beams is described, the latter in some detail. Laser fluorescence spectroscopy at high sensitivity using unpolarized bunched
beams is briefly mentioned.
KeywordsCollinear laser facilities at TRIUMF-ISAC-Spin polarized beams of 8Li +
-Collinear optical pumping-Polarized beams of 20F and 11Be
Hyperfine Interactions 04/2012; 196(1):287-294. · 0.21 Impact Factor
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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
[show abstract]
[hide abstract]
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.
Phys. Rev. B. 03/2012; 85(9).
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E Mané,
A Voss,
J A Behr,
J Billowes,
T Brunner,
F Buchinger,
J E Crawford,
J Dilling,
S Ettenauer, C D P Levy,
O Shelbaya,
M R Pearson
[show abstract]
[hide abstract]
ABSTRACT: Collinear-laser spectroscopy with the bunched-beams technique was used for the study of neutron deficient Rb isotopes, out to (74)Rb (N = Z = 37) at TRIUMF. The measured hyperfine coupling constants of (76,78m)Rb were in agreement with literature values. The nuclear spin of (75)Rb was confirmed to be I = 3/2, and its hyperfine coupling constants were measured for the first time. The mean-square charge radius of (74)Rb was determined for the first time. This result has improved the isospin symmetry breaking correction term used to calculate the Ft value, with implications for tests of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.
Physical Review Letters 11/2011; 107(21):212502. · 7.37 Impact Factor
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E. Mané,
A. Voss,
J. A. Behr,
J Billowes,
T. Brunner,
F Buchinger,
J E Crawford,
J. Dilling,
S. Ettenauer, C. D. P. Levy,
O. Shelbaya,
M. R. Pearson
[show abstract]
[hide abstract]
ABSTRACT: Collinear-laser spectroscopy with bunched-beams technique was used for the
study of neutron deficient Rb isotopes, out to $^{74}$Rb ($N=Z=37$) at TRIUMF.
The measured hyperfine coupling constants of $^{76,78m}$Rb were in agreement
with literature values. The nuclear spin of $^{75}$Rb was confirmed to be
$I=3/2$, and its hyperfine coupling constants were measured for the first time.
The mean-square charge radius of $^{74}$Rb was determined for the first time.
This result has improved the isospin symmetry breaking correction term used to
calculate the $\mathcal{F}t$ value, with implications for tests of the
unitarity of the Cabibbo-Kobayashi-Maskawa matrix.
10/2011;
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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
[show abstract]
[hide abstract]
ABSTRACT: A β-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 polarise the nuclei of interest. Recently, the β-NQR technique in a zero magnetic field has been applied for the first-time to measure ratios of static nuclear quadrupole moments of, Li. Preliminary results of the experiment determining the ratios Q9/Q8 and Q11/Q9 show agreement with present literature values with improved precision.
Journal of Physics Conference Series 09/2011; 312(9):092063.
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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
[show abstract]
[hide abstract]
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 = 0.966 75(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.
Journal of Physics G Nuclear and Particle Physics 05/2011; 38(7):075102. · 4.18 Impact Factor
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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
[show abstract]
[hide abstract]
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.
Phys. Rev. B. 02/2011; 83(5).
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W. Nörtershäuser,
R. Sánchez,
G. Ewald,
A. Dax,
J. Behr,
P. Bricault,
B. A. Bushaw,
J. Dilling,
M. Dombsky,
G. W. F. Drake, [......],
H.-J. Kluge,
Th. Kühl,
J. Lassen, C. D. P. Levy,
K. Pachucki,
M. Pearson,
M. Puchalski,
A. Wojtaszek,
Z.-C. Yan,
C. Zimmermann
[show abstract]
[hide abstract]
ABSTRACT: Changes in the mean square nuclear charge radii along the lithium isotopic chain were determined using a combination of precise isotope shift measurements and theoretical atomic structure calculations. Nuclear charge radii of light elements are of high interest due to the appearance of the nuclear halo phenomenon in this region of the nuclear chart. During the past years we have developed a laser spectroscopic approach to determine the charge radii of lithium isotopes which combines high sensitivity, speed, and accuracy to measure the extremely small field shift of an 8-ms-lifetime isotope with production rates on the order of only 10 000 atoms/s. The method was applied to all bound isotopes of lithium including the two-neutron halo isotope 11Li at the on-line isotope separators at GSI, Darmstadt, Germany, and at TRIUMF, Vancouver, Canada. We describe the laser spectroscopic method in detail, present updated and improved values from theory and experiment, and discuss the results.
Phys. Rev. A. 01/2011; 83(1).
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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
[show abstract]
[hide abstract]
ABSTRACT: Weak spontaneous magnetic fields are observed near the surface of YBCO films
using Beta-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/YBCO interface. The magnitude of the line broadening at 10 K
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.
01/2011;
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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
[show abstract]
[hide abstract]
ABSTRACT: Beta-NMR has been used to study vortex lattice disorder near the surface of
the high-Tc superconductor 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.
03/2010;
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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
[show abstract]
[hide abstract]
ABSTRACT: The electric-quadrupole coupling constant of the ground states of the proton drip line nucleus $^{20}$Na($I^{\pi}$ = 2$^{+}$, $T_{1/2}$ = 447.9 ms) and the neutron-deficient nucleus $^{21}$Na($I^{\pi}$ = 3/2$^{+}$, $T_{1/2}$ = 22.49 s) in a hexagonal ZnO single crystal were precisely measured to be $|eqQ/h| = 690 \pm 12$ kHz and 939 $\pm$ 14 kHz, respectively, using the multi-frequency $\beta$-ray detecting nuclear magnetic resonance technique under presence of an electric-quadrupole interaction. A electric-quadrupole coupling constant of $^{27}$Na in the ZnO crystal was also measured to be $|eqQ/h| = 48.4 \pm 3.8$ kHz. The electric-quadrupole moments were extracted as $|Q(^{20}$Na)$|$ = 10.3 $\pm$ 0.8 $e$ fm$^2$ and $|Q(^{21}$Na)$|$ = 14.0 $\pm$ 1.1 $e$ fm$^2$, using the electric-coupling constant of $^{27}$Na 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.
02/2009;
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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
[show abstract]
[hide abstract]
ABSTRACT: Low energy $\beta$-detected nuclear magnetic resonance ($\beta$-NMR) was used to investigate the spatial dependence of the hyperfine magnetic fields induced by Fe in the nonmagnetic Ag of an Au(40 \AA)/Ag(200 \AA)/Fe(140 \AA) (001) magnetic multilayer (MML) grown on GaAs. The resonance lineshape in the Ag layer shows dramatic broadening compared to intrinsic Ag. This broadening is attributed to large induced magnetic fields 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. Comment: 5 pages, 4 figure. To be published in Phys. Rev. B
03/2008;
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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
[show abstract]
[hide abstract]
ABSTRACT: The magnetic properties of a monolayer of Mn12 single molecule magnets grafted onto a silicon (Si) substrate have been investigated using depth-controlled beta-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.
Nano Letters 07/2007; 7(6):1551-5. · 13.20 Impact Factor
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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
[show abstract]
[hide abstract]
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 beta-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.
Physical Review Letters 05/2007; 98(16):167001. · 7.37 Impact Factor
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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
[show abstract]
[hide abstract]
ABSTRACT: A low energy radioactive beam of polarized $^8$Li has been used to observe the vortex lattice near the surface of superconducting NbSe$_2$. The inhomogeneous magnetic field distribution associated with the vortex lattice was measured using depth-resolved $\beta$-detected NMR. Below $T_c$ one observes the characteristic lineshape 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 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.
04/2007;
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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
[show abstract]
[hide abstract]
ABSTRACT: Depth-controlled $\beta$-NMR was used to study highly spin-polarized $^8$Li in a Cu film of thickness 100 nm deposited onto a MgO substrate. The positive Knight Shifts and spin relaxation data show that $^8$Li occupies two sites at low temperatures, assigned to be the substitutional ($S$) and octahedral ($O$) interstitial sites. Between 50 to 100 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.
01/2007;
