487 research outputs found
Magnetic studies on the metallic perovskite-type compound Mn 3SnN
Mn3SnN is a metallic compound of perovskite-type structure which shows four different crystallographic and magnetically ordered phases. From neutron diffraction data, magnetic measurements and Mössbauer experiments performed at different temperatures it is concluded that the magnetic properties depend critically on the existence of singularities in the density of states.Le composé métallique Mn3SnN de structure-type pérovskite présente quatre phases cristallographiques et magnétiques ordonnées différentes. Les expériences de diffraction neutronique, les mesures magnétiques et la spectroseopie Mössbauer effectuées en fonction de la température font apparaître un comportement critique des propriétés magnétiques révélant l'existence de singularités dans la densité d'états
Computation of topological phase diagram of disordered PbSnTe using the kernel polynomial method
We present an algorithm to determine topological invariants of inhomogeneous
systems, such as alloys, disordered crystals, or amorphous systems. Based on
the kernel polynomial method, our algorithm allows us to study samples with
more than degrees of freedom. Our method enables the study of large
complex compounds, where disorder is inherent to the system. We use it to
analyse PbSnTe and tighten the critical concentration for the
phase transition.Comment: 4 pages + supplemental materia
X-ray photoelectron emission microscopy in combination with x-ray magnetic circular dichroism investigation of size effects on field-induced N\'eel-cap reversal
X-ray photoelectron emission microscopy in combination with x-ray magnetic
circular dichroism is used to investigate the influence of an applied magnetic
field on N\'eel caps (i.e., surface terminations of asymmetric Bloch walls).
Self-assembled micron-sized Fe(110) dots displaying a moderate distribution of
size and aspect ratios serve as model objects. Investigations of remanent
states after application of an applied field along the direction of N\'eel-cap
magnetization give clear evidence for the magnetization reversal of the N\'eel
caps around 120 mT, with a 20 mT dispersion. No clear correlation could be
found between the value of the reversal field and geometrical features of the
dots
Hidden spin liquid in an antiferromagnet: Applications to FeCrAs
The recently studied material FeCrAs exhibits a surprising combination of
experimental signatures, with metallic, Fermi liquid like specific heat but
resistivity showing strong non-metallic character. The Cr sublattice posseses
local magnetic moments, in the form of stacked (distorted) Kagome lattices.
Despite the high degree of magnetic frustration, anti-ferromagnetic order
develops below ~125K suggesting the non-magnetic Fe sublattice may play a role
in stabilizing the ordering. From the material properties we propose a
microscopic Hamiltonian for the low energy degrees of freedom, including the
non-magnetic Fe sublattice, and study its properties using slave-rotor mean
field theory. Using this approach we find a spin liquid phase on the Fe
sublattice, which survives even in the presence of the magnetic Cr sublattice.
Finally, we suggest that the features of FeCrAs can be qualitatively explained
by critical fluctuations in the non-magnetic sublattice Fe due to proximity to
a metal-insulator transition.Comment: 9 pages, 8 figure
Two Gap State Density in MgB: A True Bulk Property or A Proximity Effect?
We report on the temperature dependence of the quasiparticle density of
states (DOS) in the simple binary compound MgB2 directly measured using
scanning tunneling microscope (STM). To achieve high quality tunneling
conditions, a small crystal of MgB2 is used as a tip in the STM experiment. The
``sample'' is chosen to be a 2H-NbSe2 single crystal presenting an atomically
flat surface. At low temperature the tunneling conductance spectra show a gap
at the Fermi energy followed by two well-pronounced conductance peaks on each
side. They appear at voltages V mV and V mV. With rising temperature both peaks disappear at the Tc of the bulk
MgB2, a behavior consistent with the model of two-gap superconductivity. The
explanation of the double-peak structure in terms of a particular proximity
effect is also discussed.Comment: 4 pages, 3 figure
Angular-dependence of magnetization switching for a multi-domain dot: experiment and simulation
We have measured the in-plane angular variation of nucleation and
annihilation fields of a multi-domain magnetic single dot with a microsquid.
The dots are Fe/Mo(110) self-assembled in UHV, with sub-micron size and a
hexagonal shape. The angular variations were quantitatively reproduced by
micromagnetic simulations. Discontinuities in the variations are observed, and
shown to result from bifurcations related to the interplay of the non-uniform
magnetization state with the shape of the dot.Comment: 4 pages, 4 figures, for submission as a regular articl
Ferromagnetic (Ga,Mn)N epilayers versus antiferromagnetic GaMnN clusters
Mn-doped wurtzite GaN epilayers have been grown by nitrogen plasma-assisted
molecular beam epitaxy. Correlated SIMS, structural and magnetic measurements
show that the incorporation of Mn strongly depends on the conditions of the
growth. Hysteresis loops which persist at high temperature do not appear to be
correlated to the presence of Mn. Samples with up to 2% Mn are purely
substitutional GaMnN epilayers, and exhibit paramagnetic
properties. At higher Mn contents, precipitates are formed which are identified
as GaMnN clusters by x-ray diffraction and absorption: this induces a
decrease of the paramagnetic magnetisation. Samples co-doped with enough Mg
exhibit a new feature: a ferromagnetic component is observed up to
K, which cannot be related to superparamagnetism of unresolved magnetic
precipitates.Comment: Revised versio
Artificial Kagome Arrays of Nanomagnets: A Frozen Dipolar Spin Ice
Magnetic frustration effects in artificial kagome arrays of nanomagnets are
investigated using x-ray photoemission electron microscopy and Monte Carlo
simulations. Spin configurations of demagnetized networks reveal unambiguous
signatures of long range, dipolar interaction between the nanomagnets. As soon
as the system enters the spin ice manifold, the kagome dipolar spin ice model
captures the observed physics, while the short range kagome spin ice model
fails.Comment: 4 pages, 4 figures, 1 tabl
Controlled switching of N\'eel caps in flux-closure magnetic dots
While magnetic hysteresis usually considers magnetic domains, the switching
of the core of magnetic vortices has recently become an active topic. We
considered Bloch domain walls, which are known to display at the surface of
thin films flux-closure features called N\'eel caps. We demonstrated the
controlled switching of these caps under a magnetic field, occurring via the
propagation of a surface vortex. For this we considered flux-closure states in
elongated micron-sized dots, so that only the central domain wall can be
addressed, while domains remain unaffected.Comment: 4 pages, 3 figure
Growth modes of Fe(110) revisited: a contribution of self-assembly to magnetic materials
We have revisited the epitaxial growth modes of Fe on W(110) and Mo(110), and
propose an overview or our contribution to the field. We show that the
Stranski-Krastanov growth mode, recognized for a long time in these systems, is
in fact characterized by a bimodal distribution of islands for growth
temperature in the range 250-700°C. We observe firstly compact islands
whose shape is determined by Wulff-Kaischev's theorem, secondly thin and flat
islands that display a preferred height, ie independant from nominal thickness
and deposition procedure (1.4nm for Mo, and 5.5nm for W on the average). We
used this effect to fabricate self-organized arrays of nanometers-thick stripes
by step decoration. Self-assembled nano-ties are also obtained for nucleation
of the flat islands on Mo at fairly high temperature, ie 800°C. Finally,
using interfacial layers and solid solutions we separate two effects on the
preferred height, first that of the interfacial energy, second that of the
continuously-varying lattice parameter of the growth surface.Comment: 49 pages. Invited topical review for J. Phys.: Condens. Matte
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