252 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
Mesoscopic correlations in Tb2Ti2O7 spin liquid
We have studied the spin correlations with = (, ,
) propagation vector which appear below 0.4\, K in \tbti\ spin liquid
by combining powder neutron diffraction and specific heat on
TbTiO samples with =0, 0.01, -0.01. The =
(, , ) order clearly appears on all neutron patterns
by subtracting a pattern at 1.2(1)\,K. Refining the subtracted patterns at
0.07\,K yields two possible spin structures, with spin-ice-like and
monopole-like correlations respectively. Mesoscopic correlations involve Tb
moments of 1 to 2 \mub\ ordered on a length scale of about 20 \AA. In addition,
long range order involving a small spin component of 0.1 to 0.2 \mub\ is
detected for the = 0 and 0.01 samples showing a peak in the specific heat.
Comparison with previous single crystals data suggests that the (,
, ) order settles in through nanometric spin textures with
dominant spin ice character and correlated orientations, analogous to
nanomagnetic twins
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
Growth inhibition of an Araucaria angustifolia (Coniferopsida) fungal seed pathogen, Neofusicoccum parvum, by soil streptomycetes
Background: Araucariaceae are important forest trees of the southern hemisphere. Life expectancy of their seedlings can largely be reduced by fungal infections. In this study we have isolated and characterized such a fungus and investigated the potentia
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
Cohérence et complexité : structures et via expositionis dans la grammaire philosophique de Jean-Marie Zemb
Jean-Marie Zemb\u27s philosophical grammar intends to serve epistemological goals and to build a linguistic science that is based on observation and explanation and focused on the deep realms of thought. Nourished by the philosophical and linguistic traditions of France and Germany, the two countries in which he was educated, Zemb is one of the essential French linguists concerned with contemporary epstemology. He can be compared to Eugenio Coseriu. His French-German comparative grammars do not propose a "system," but instead "rectify" the errors inherited from both earlier and contemporary French and German linguistic theories. This article outlines his epistemological approach and discusses several specific examples. Among the key words of his linguistic oeuvre are "archi-lexeme," "meaning quanta," "thema," "rhema," and "phema.
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
Structure and magnetic order in Fe2+xV1-xAl
We present a detailed structural investigation via neutron diffraction of
differently heat treated samples Fe2VAl and Fe2+xV1-xAl. Moreover, the magnetic
behaviour of these materials is studied by means of mSR and
Mossbauer-experiments. Our structural investigation indicates that quenched
Fe2VAl, exhibiting the previously reported "Kondo insulating like" behaviour,
is off-stoichiometric (6%) in its Al content. Slowly cooled Fe2VAl is
structurally better ordered and stoichiometric, and the microscopic magnetic
probes establish long range ferromagnetic order below TC = 13K, consistent with
results from bulk experiments. The magnetic state can be modelled as being
generated by diluted magnetic ions in a non-magnetic matrix. Quantitatively,
the required number of magnetic ions is too large as to be explained by a model
of Fe/V site exchange. We discuss the implications of our findings for the
ground state properties of Fe2VAl, in particular with respect to the role of
crystallographic disorder.Comment: accepted for publication in J. Phys.: Condens. Matte
Topics in coarsening phenomena
These lecture notes give a very short introduction to coarsening phenomena
and summarize some recent results in the field. They focus on three aspects:
the super-universality hypothesis, the geometry of growing structures, and
coarsening in the spiral kinetically constrained model.Comment: Lecture notes. Fundamental Problems in Statistical Physics XII,
Leuven, Aug 30 - Sept 12, 200
Well dispersed fractal aggregates as filler in polymer-silica nanocomposites: long range effects in rheology
We are presenting a new method of processing polystyrene-silica
nanocomposites, which results in a very well-defined dispersion of small
primary aggregates (assembly of 15 nanoparticles of 10 nm diameter) in the
matrix. The process is based on a high boiling point solvent, in which the
nanoparticles are well dispersed, and controlled evaporation. The filler's fine
network structure is determined over a wide range of sizes, using a combination
of Small Angle Neutron Scattering (SANS) and Transmission Electronic Microscopy
(TEM). The mechanical response of the nanocomposite material is investigated
both for small (ARES oscillatory shear and Dynamical Mechanical Analysis) and
large deformations (uniaxial traction), as a function of the concentration of
the particles. We can investigate the structure-property correlations for the
two main reinforcement effects: the filler network contribution, and a
filler-polymer matrix effect. Above a silica volume fraction threshold, we see
a divergence of the modulus correlated to the build up of a connected network.
Below the threshold, we obtain a new additional elastic contribution of much
longer terminal time than the matrix. Since aggregates are separated by at
least 60 nm, this new filler-matrix contribution cannot be described solely
with the concept of glassy layer (2nm)
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