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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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A Charnukha,
A Cvitkovic,
T Prokscha,
D Pröpper,
N Ocelic,
A Suter, Z Salman,
E Morenzoni,
J Deisenhofer,
V Tsurkan,
A Loidl,
B Keimer,
A V Boris
[show abstract]
[hide abstract]
ABSTRACT: We studied phase separation in the single-crystalline antiferromagnetic superconductor Rb_{2}Fe_{4}Se_{5} (RFS) using a combination of scattering-type scanning near-field optical microscopy and low-energy muon spin rotation (LE-μSR). We demonstrate that the antiferromagnetic and superconducting phases segregate into nanometer-thick layers perpendicular to the iron-selenide planes, while the characteristic in-plane size of the metallic domains reaches 10 μm. By means of LE-μSR we further show that in a 40-nm thick surface layer the ordered antiferromagnetic moment is drastically reduced, while the volume fraction of the paramagnetic phase is significantly enhanced over its bulk value. Self-organization into a quasiregular heterostructure indicates an intimate connection between the modulated superconducting and antiferromagnetic phases.
Physical Review Letters 07/2012; 109(1):017003. · 7.37 Impact Factor
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A Antognini,
P Crivelli,
T Prokscha,
K S Khaw,
B Barbiellini,
L Liszkay,
K Kirch,
K Kwuida,
E Morenzoni,
F M Piegsa, Z Salman,
A Suter
[show abstract]
[hide abstract]
ABSTRACT: We report on muonium (Mu) emission into vacuum following μ(+) implantation in mesoporous thin SiO(2) films. We obtain a yield of Mu into vacuum of (38±4)% at 250 K and (20±4)% at 100 K for 5 keV μ(+) implantation energy. From the implantation energy dependence of the Mu vacuum yield we determine the Mu diffusion constants in these films: D(Mu)(250 K)=(1.6±0.1)×10(-4) cm(2)/s and D(Mu)(100 K)=(4.2±0.5)×10(-5) cm(2)/s. Describing the diffusion process as quantum mechanical tunneling from pore to pore, we reproduce the measured temperature dependence ∼T(3/2) of the diffusion constant. We extract a potential barrier of (-0.3±0.1) eV which is consistent with our computed Mu work function in SiO(2) of [-0.3,-0.9] eV. The high Mu vacuum yield, even at low temperatures, represents an important step toward next generation Mu spectroscopy experiments.
Physical Review Letters 04/2012; 108(14):143401. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present a detailed investigation of the magnetic and structural properties
of magnetically doped 3D topological insulator Bi2Se3. From muon spin
relaxation measurements in zero magnetic field, we find that even 5% Fe doping
on the Bi site turns the full volume of the sample magnetic at temperatures as
high as ~250 K. This is also confirmed by magnetization measurements. Two
magnetic "phases" are identified; the first is observed between ~10-250 K while
the second appears below ~10 K. These cannot be attributed to impurity phases
in the samples. We discuss the nature and details of the observed magnetism and
its dependence on doping level.
03/2012;
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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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A. Charnukha,
A. Cvitkovic,
T. Prokscha,
D. Pröpper,
N. Ocelic,
A. Suter, Z. Salman,
E. Morenzoni,
J. Deisenhofer,
V. Tsurkan,
A. Loidl,
B. Keimer,
A. V. Boris
[show abstract]
[hide abstract]
ABSTRACT: We studied phase separation in a single-crystalline antiferromagnetic
superconductor Rb2Fe4Se5 (RFS) using a combination of scattering-type scanning
near-field optical microscopy (s-SNOM) and low-energy muon spin rotation
(LE-\mu SR). We demonstrate that the antiferromagnetic and superconducting
phases segregate into nanometer-thick layers perpendicular to the iron-selenide
planes, while the characteristic in-plane size of the metallic domains reaches
10 \mu m. By means of LE-\mu SR we further show that in a 40-nm thick surface
layer the ordered antiferromagnetic moment is drastically reduced, while the
volume fraction of the paramagnetic phase is significantly enhanced over its
bulk value. Self-organization into a quasiregular heterostructure indicates an
intimate connection between the modulated superconducting and antiferromagnetic
phases.
02/2012;
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Oren Ofer,
J. C. Baglo,
M. D. Hossain,
R. F. Kiefl,
W. N. Hardy,
A. Thaler,
H. Kim,
M. A. Tanatar,
P. C. Canfield,
R. Prozorov,
G. M. Luke,
E. Morenzoni,
H. Saadaoui,
A. Suter,
T. Prokscha,
B. M. Wojek, Z. Salman
Physical Review B. 01/2012; 85(6):060506.
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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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[show abstract]
[hide abstract]
ABSTRACT: We present a method to measure the magnetic properties of monolayers and
ultra-thin films of magnetic material. The method is based on low energy muon
spin rotation and $\beta$-detected nuclear magnetic resonance measurements. A
spin probe is used as a "proximal" magnetometer by implanting it in the
substrate, just below the magnetic material. We calculate the expected magnetic
field distribution sensed by the probe and discuss its temperature and
implantation depth dependencies. This method is highly suitable for measuring
the magnetic properties of monolayers of single molecule magnets, but can also
be extended to ultra-thin magnetic films.
08/2011;
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J. S. Lord,
I. McKenzie,
P. J. Baker,
S. J. Blundell,
S. P. Cottrell,
S. R. Giblin,
J. Good,
A. D. Hillier,
B. H. Holsman,
P. J. C. King,
T. Lancaster,
R. Mitchell,
J. B. Nightingale,
M. Owczarkowski,
S. Poli,
F. L. Pratt,
N. J. Rhodes,
R. Scheuermann, Z. Salman
[show abstract]
[hide abstract]
ABSTRACT: The high magnetic field (HiFi) muon instrument at the ISIS pulsed neutron and muon source is a state-of-the-art spectrometer designed to provide applied magnetic fields up to 5 T for muon studies of condensed matter and molecular systems. The spectrometer is optimised for time-differential muon spin relaxation studies at a pulsed muon source. We describe the challenges involved in its design and construction, detailing, in particular, the magnet and detector performance. Commissioning experiments have been conducted and the results are presented to demonstrate the scientific capabilities of the new instrument.
Review of Scientific Instruments 07/2011; 82(7):073904-073904-10. · 1.37 Impact Factor
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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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A V Boris,
Y Matiks,
E Benckiser,
A Frano,
P Popovich,
V Hinkov,
P Wochner,
M Castro-Colin,
E Detemple,
V K Malik,
C Bernhard,
T Prokscha,
A Suter, Z Salman,
E Morenzoni,
G Cristiani,
H-U Habermeier,
B Keimer
[show abstract]
[hide abstract]
ABSTRACT: The competition between collective quantum phases in materials with strongly correlated electrons depends sensitively on the dimensionality of the electron system, which is difficult to control by standard solid-state chemistry. We have fabricated superlattices of the paramagnetic metal lanthanum nickelate (LaNiO(3)) and the wide-gap insulator lanthanum aluminate (LaAlO(3)) with atomically precise layer sequences. We used optical ellipsometry and low-energy muon spin rotation to show that superlattices with LaNiO(3) as thin as two unit cells undergo a sequence of collective metal-insulator and antiferromagnetic transitions as a function of decreasing temperature, whereas samples with thicker LaNiO(3) layers remain metallic and paramagnetic at all temperatures. Metal-oxide superlattices thus allow control of the dimensionality and collective phase behavior of correlated-electron systems.
Science 05/2011; 332(6032):937-40. · 31.20 Impact Factor
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[show abstract]
[hide abstract]
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.
05/2011;
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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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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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[show abstract]
[hide abstract]
ABSTRACT: We present zero field muon spin lattice relaxation measurements of a Dysprosium triangle molecular magnet. The local magnetic fields sensed by the implanted muons indicate the coexistence of static and dynamic internal magnetic fields below T∗∼35 K. Bulk magnetization and heat capacity measurements show no indication of magnetic ordering below this temperature. We attribute the static fields to the slow relaxation of the magnetization in the ground state of Dy3. The fluctuation time of the dynamic part of the field is estimated to be ∼0.55 μs at low temperatures.
Phys. Rev. B. 11/2010; 82(17).
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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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T Lancaster,
S J Blundell,
F L Pratt,
I. Franke,
A. J. Steele,
P. J. Baker, Z. Salman,
C. Baines,
I Watanabe,
S Carretta,
G. A. Timco,
R. E. P. Winpenny
[show abstract]
[hide abstract]
ABSTRACT: We address the cause of the unusual muon spin relaxation (muSR) results on molecular nanomagnets (MNMs). Through measurements on protonated and deuterated samples of the MNMs Cr7Mn (S=1) and Cr8 (S=0), we show that the muon spin for $S \neq 0$ MNMs is relaxed via dynamic fluctuations of the electronic spins. A freezing out of dynamic processes occurs on cooling and at low temperatures the muon spins are relaxed by the electronic spins which themselves are dephased by incoherent nuclear field fluctuations.We observe a transition to a state of static magnetic order of the MNM electronic spins in Cr7Mn below 2 K. Comment: 4 pages, 3 figures
11/2009;
