3,384 research outputs found
Possible Quantum Diffusion of Polaronic Muons in DyTiO Spin Ice
We interpret recent measurements of the zero field muon relaxation rate in
the frustrated magnetic pyrochlore DyTiO as resulting from the
quantum diffusion of muons in the substance. In this scenario, the plateau
observed at low temperature ( K) in the relaxation rate is due to coherent
tunneling of the muons through a spatially disordered spin state and not to any
magnetic fluctuations persisting at low temperature. Two further regimes either
side of a maximum relaxation rate at K correspond to a crossover
between tunnelling and incoherent activated hopping motion of the muon. Our fit
of the experimental data is compared with the case of muonium diffusion in KCl.Comment: 15 pages, 2 figure
Magnetism in heavy-fermion U(Pt,Pd)3 studied by mSR
We report mSR experiments carried out on a series of heavy-electron
pseudobinary compounds U(Pt1-xPdx)3 (x<=0.05). For x<=0.005 the zero-field muon
depolarisation is described by the Kubo-Toyabe function. However the
temperature variation of the Kubo-Toyabe relaxation rate does not show any sign
of the small-moment antiferromagnetic phase with TN~6 K (signalled by neutron
diffraction), in contrast to previous reports. The failure to detect the small
ordered moment suggests it has a fluctuating (> 10 MHz) nature, which is
consistent with the interpretation of NMR data. For 0.01<=x<=0.05 the muon
depolarisation in the ordered state is described by two terms of equal
amplitude: an exponentially damped spontaneous oscillation and a Lorentzian
Kubo-Toyabe function. These terms are associated with antiferromagnetic order
with substantial moments. The Knight-shift measured in a magnetic field of 0.6
T on single-crystalline U(Pt0.95Pd0.05)3 in the paramagnetic state shows two
signals for B perpendicular to c, while only one signal is observed for B||c.
The observation of two signals for B perpendicular to c, while there is only
one muon localisation site (0,0,0), points to the presence of two spatially
distinct regions of different magnetic response.Comment: 25 pages including 12 figures (PS), J. Phys.: Condens. Matter, in
prin
Possible Magnetic Chirality in Optically Chiral Magnet [Cr(CN)][Mn()-pnH(HO)](HO) Probed by Muon Spin Rotation and Relaxation
Local magnetic fields in a molecule-based optically chiral magnet
[Cr(CN)][Mn()-pnH(HO)](HO) (GN-S) and its enantiomer (GN-R) are
studied by means of muon spin rotation and relaxation (muSR). Detailed analysis
of muon precession signals under zero field observed below T_c supports the
average magnetic structure suggested by neutron powder diffraction. Moreover,
comparison of muSR spectra between GN-S and GN-R suggests that they are a pair
of complete optical isomers in terms of both crystallographic and magnetic
structure. Possibility of magnetic chirality in such a pair is discussed.Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jp
Pressure Induced Static Magnetic Order in Superconducting FeSe_1-x
We report on a detailed investigation of the electronic phase diagram of
FeSe_1-x under pressures up to 1.4GPa by means of AC magnetization and
muon-spin rotation. At a pressure \simeq0.8GPa the non-magnetic and
superconducting FeSe_1-x enters a region where long range static magnetic order
is realized above T_c and bulk superconductivity coexists and competes on short
length scales with the magnetic order below T_c. For even higher pressures an
enhancement of both the magnetic and the superconducting transition
temperatures as well as of the corresponding order parameters is observed.
These exceptional properties make FeSe1-x to be one of the most interesting
superconducting systems investigated extensively at present.Comment: 5 pages, 3 figure
Muon-spin-rotation measurements of the penetration depth in Li_2Pd_3B
Measurements of the magnetic field penetration depth in the ternary
boride superconductor LiPdB ( K) have been carried out by
means of muon-spin rotation (SR). The absolute values of , the
Ginzburg-Landau parameter , and the first and the second
critical fields at T=0 obtained from SR were found to be
nm, , mT, and
T, respectively. The zero-temperature value of the
superconducting gap 1.31(3) meV was found, corresponding to the
ratio . At low temperatures saturates and
becomes constant below , in agreement with what is expected for
s-wave BCS superconductors. Our results suggest that LiPdB is a s-wave
BCS superconductor with the only one isotropic energy gap.Comment: 6 pages, 7 figure
Magnetic order in double-layer manganites (La(1-z)Pr(z))1.2Sr1.8Mn2O7: intrinsic properties and role of the intergrowths
We report on an investigation of the double-layer manganite series
(La(1-z)Pr(z))1.2Sr1.8Mn2O7 (0 <= z <= 1), carried out on single crystals by
means of both macroscopic magnetometry and local probes of magnetism (muSR,
55Mn NMR). Muons and NMR demonstrate an antiferromagnetically ordered ground
state at non-ferromagnetic compositions (z >= 0.6), while more moderate Pr
substitutions (0.2 <= z <= 0.4) induce a spin reorientation transition within
the ferromagnetic phase.
A large magnetic susceptibility is detected at {Tc,TN} < T < 250K at all
compositions. From 55Mn NMR spectroscopy, such a response is unambiguously
assigned to the intergrowth of a ferromagnetic pseudocubic phase
(La(1-z)Pr(z))(1-x)Sr(x)MnO3, with an overall volume fraction estimated as
0.5-0.7% from magnetometry. Evidence is provided for the coupling of the
magnetic moments of these inclusions with the magnetic moments of the
surrounding (La(1-z)Pr(z))1.2Sr1.8Mn2O7 phase, as in the case of finely
dispersed impurities. We argue that the ubiquitous intergrowth phase may play a
role in the marked first-order character of the magnetic transition and the
metamagnetic properties above Tc reported for double-layer manganites.Comment: 11 pages, 9 figures. Submitted to Phys. Rev.
Euler characteristic of coherent sheaves on simplicial torics via the Stanley-Reisner ring
We combine work of Cox on the total coordinate ring of a toric variety and
results of Eisenbud-Mustata-Stillman and Mustata on cohomology of toric and
monomial ideals to obtain a formula for computing the Euler characteristic of a
Weil divisor D on a complete simplicial toric variety in terms of graded pieces
of the Cox ring and Stanley-Reisner ring. The main point is to use Alexander
duality to pass from the toric irrelevant ideal, which appears in the
computation of the Euler characteristic of D, to the Stanley-Reisner ideal of
the fan, which is used in defining the Chow ring. The formula also follows from
work of Maclagan-Smith.Comment: 9 pages 1 figur
Evidence for a two component magnetic response in UPt3
The magnetic response of the heavy fermion superconductor UPt_3 has been
investigated on a microscopic scale by muon Knight shift studies. Two distinct
and isotropic Knight shifts have been found for the field in the basal plane.
While the volume fractions associated with the two Knight shifts are
approximately equal at low and high temperatures, they show a dramatic and
opposite temperature dependence around T_N. Our results are independent on the
precise muon localization site. We conclude that UPt_3 is characterized by a
two component magnetic response.Comment: 5 pages, 4 figure
Penetration depth, multiband superconductivity, and absence of muon-induced perturbation in superconducting PrOsSb
Transverse-field muon spin rotation (SR) experiments in the
heavy-fermion superconductor PrOsSb ( K) suggest that
the superconducting penetration depth is temperature-independent
at low temperatures, consistent with a gapped quasiparticle excitation
spectrum. In contrast, radiofrequency (rf) inductive measurements yield a
stronger temperature dependence of , indicative of point nodes in
the gap. This discrepancy appears to be related to the multiband structure of
PrOsSb. Muon Knight shift measurements in PrOsSb
suggest that the perturbing effect of the muon charge on the neighboring
Pr crystalline electric field is negligibly small, and therefore is
unlikely to cause the difference between the SR and rf results.Comment: 10 pages, 7 figure
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