424 research outputs found
Zero field muon spin lattice relaxation rate in a Heisenberg ferromagnet at low temperature
We provide a theoretical framework to compute the zero field muon spin
relaxation rate of a Heisenberg ferromagnet at low temperature. We use the
linear spin wave approximation. The rate, which is a measure of the spin
lattice relaxation induced by the magnetic fluctuations along the easy axis,
allows one to estimate the magnon stiffness constant.Comment: REVTeX 3.0 manuscript, 5 pages, no figure. Published in Phys. Rev. B
52, 9155 (1995
Comparison of different methods for analyzing SR line shapes in the vortex state of type-II superconductors
A detailed analysis of muon-spin rotation (SR) spectra in the vortex
state of type-II superconductors using different theoretical models is
presented. Analytical approximations of the London and Ginzburg-Landau (GL)
models, as well as an exact solution of the GL model were used. The limits of
the validity of these models and the reliability to extract parameters such as
the magnetic penetration depth and the coherence length from
the experimental SR spectra were investigated. The analysis of the
simulated SR spectra showed that at high magnetic fields there is a strong
correlation between obtained and for any value of the
Ginzburg-Landau parameter . The smaller the applied
magnetic field is, the smaller is the possibility to find the correct value of
. A simultaneous determination of and without any
restrictions is very problematic, independent of the model used to describe the
vortex state. It was found that for extreme type-II superconductors and low
magnetic fields, the fitted value of is practically independent of
. The second-moment method frequently used to analyze SR spectra by
means of a multi-component Gaussian fit, generally yields reliable values of
in the whole range of applied fields
( and are the first and second critical fields, respectively).
These results are also relevant for the interpretation of small-angle neutron
scattering (SANS) experiments of the vortex state in type-II superconductors.Comment: 17 pages, 19 figure
2D Kagome Ordering in the 3D Frustrated Spinel Li2Mn2O4
muSR experiments on the geometrically frustrated spinel oxide, Li2Mn2O4, show
the development of spin correlations over a range of length scales with
decreasing temperature. Increased relaxation below 150 K is consistent with the
onset of spin correlations. Below 50 K, spin order on a length scale, which is
long range for the muSR probe, appears abruptly in temperature, consistent with
prior neutron diffraction results. The oscillations in the zero field asymmetry
are analyzed using a three frequency model. By locating the muon site this is
shown to be consistent with the unexpected 2D q = root 3 x root 3 structure on
the Kagome planes proposed originally from neutron data. Longitudinal field
data demonstrate that some spin dynamics persist even at 2 K. Thus, a very
complex magnetic ground state, featuring the co-existence of long length scale
2D ordering and significant spin dynamics, is proposed. This is unusual
considering the 3D topology of the Mn3+ spins in this material.Comment: 9 pages, 9 figures, to be submitted to J. Phys. Cond. Mat
Muon spin rotation and relaxation in magnetic materials
A review of the muon spin rotation and relaxation (SR) studies on
magnetic materials published from July 1993 is presented. It covers the
investigation of magnetic phase diagrams, of spin dynamics and the analysis of
the magnetic properties of superconductors. We have chosen to focus on selected
experimental works in these different topics. In addition, a list of published
works is provided.Comment: Review article, 59 pages, LaTeX with IoP macro
Understanding the SR spectra of MnSi without magnetic polarons
Transverse-field muon-spin rotation (SR) experiments were performed on a
single crystal sample of the non-centrosymmetric system MnSi. The observed
angular dependence of the muon precession frequencies matches perfectly the one
of the Mn-dipolar fields acting on the muons stopping at a 4a position of the
crystallographic structure. The data provide a precise determination of the
magnetic dipolar tensor. In addition, we have calculated the shape of the field
distribution expected below the magnetic transition temperature at the 4a
muon-site when no external magnetic field is applied. We show that this field
distribution is consistent with the one reported by zero-field SR studies.
Finally, we present ab initio calculations based on the density-functional
theory which confirm the position of the muon stopping site inferred from
transverse-field SR. In view of the presented evidence we conclude that
the SR response of MnSi can be perfectly and fully understood without
invoking a hypothetical magnetic polaron state.Comment: 10 pages, 12 figure
Finite deformations govern the anisotropic shear-induced area reduction of soft elastic contacts
Solid contacts involving soft materials are important in mechanical
engineering or biomechanics. Experimentally, such contacts have been shown to
shrink significantly under shear, an effect which is usually explained using
adhesion models. Here we show that quantitative agreement with recent high-load
experiments can be obtained, with no adjustable parameter, using a non-adhesive
model, provided that finite deformations are taken into account. Analysis of
the model uncovers the basic mechanisms underlying shear-induced area
reduction, local contact lifting being the dominant one. We confirm
experimentally the relevance of all those mechanisms, by tracking the
shear-induced evolution of tracers inserted close to the surface of a smooth
elastomer sphere in contact with a smooth glass plate. Our results suggest that
finite deformations are an alternative to adhesion, when interpreting a variety
of sheared contact experiments involving soft materials.Comment: Version accepted at J. Mech. Phys. Solids. It includes Supplementary
Informatio
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
Magnetoresistance of UPt3
We have performed measurements of the temperature dependence of the
magnetoresistance up to 9 T in bulk single crystals of UPt3 with the magnetic
field along the b axis, the easy magnetization axis. We have confirmed previous
results for transverse magnetoresistance with the current along the c axis, and
report measurements of the longitudinal magnetoresistance with the current
along the b axis. The presence of a linear term in both cases indicates broken
orientational symmetry associated with magnetic order. With the current along
the c axis the linear term appears near 5 K, increasing rapidly with decreasing
temperature. For current along the b axis the linear contribution is negative.Comment: 6 pages, 3 figures, submitted to Quantum Fluids and Solids Conference
(QFS 2006
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