167 research outputs found
Thermodynamic investigations in the precursor region of FeGe
High-resolution DC magnetization and AC-specific heat data of the cubic
helimagnet FeGe have been measured as function of temperature and magnetic
field. The magnetization data as well as the isothermal susceptibility data
confirm the complexity of the magnetic phase diagram in the vicinity of the
onset of long-rang magnetic order (Tc = 278.5 K) and the existence of a
segmented A-phase region. Moreover, these data revealed independent and clear
indications of phase boundaries and crossovers within the A-phase region.
Together with the anomalies in the specific-heat data around Tc and at small
magnetic fields (H < 600 Oe) a complex magnetic phase diagram of FeGe is
obtained.Comment: Presented at the QCNP conference in Dreden, Germany, August 201
Superconductivity in doped sp3 semiconductors: The case of the clathrates
We present a joint experimental and theoretical study of the superconductivity in doped silicon clathrates. The critical temperature in Ba-8@Si-46 is shown to strongly decrease with applied pressure. These results are corroborated by ab initio calculations using MacMillan's formulation of the BCS theory with the electron-phonon coupling constant lambda calculated from perturbative density functional theory. Further, the study of I-8@Si-46 and of gedanken pure silicon diamond and clathrate phases doped within a rigid-band approach show that the superconductivity is an intrinsic property of the sp(3) silicon network. As a consequence, carbon clathrates are predicted to yield large critical temperatures with an effective electron-phonon interaction much larger than in C-60
Chiral skyrmions in thin magnetic films: new objects for magnetic storage technologies?
Axisymmetric magnetic lines of nanometer sizes (chiral vortices or skyrmions)
have been predicted to exist in a large group of noncentrosymmetric crystals
more than two decades ago. Recently these magnetic textures have been directly
observed in nanolayers of cubic helimagnets and monolayers of magnetic metals.
We develop a micromagnetic theory of chiral skyrmions in thin magnetic layers
for magnetic materials with intrinsic and induced chirality. Such particle-like
and stable micromagnetic objects can exist in broad ranges of applied magnetic
fields including zero field. Chiral skyrmions can be used as a new type of
highly mobile nanoscale data carriers
Interesting magnetic properties of FeCoSi alloys
Solid solution between nonmagnetic narrow gap semiconductor FeSi and
diamagnetic semi-metal CoSi gives rise to interesting metallic alloys with
long-range helical magnetic ordering, for a wide range of intermediate
concentration. We report various interesting magnetic properties of these
alloys, including low temperature re-entrant spin-glass like behaviour and a
novel inverted magnetic hysteresis loop. Role of Dzyaloshinski-Moriya
interaction in the magnetic response of these non-centrosymmetric alloys is
discussed.Comment: 11 pages and 3 figure
Doping a semiconductor to create an unconventional metal
Landau Fermi liquid theory, with its pivotal assertion that electrons in
metals can be simply understood as independent particles with effective masses
replacing the free electron mass, has been astonishingly successful. This is
true despite the Coulomb interactions an electron experiences from the host
crystal lattice, its defects, and the other ~1022/cm3 electrons. An important
extension to the theory accounts for the behaviour of doped semiconductors1,2.
Because little in the vast literature on materials contradicts Fermi liquid
theory and its extensions, exceptions have attracted great attention, and they
include the high temperature superconductors3, silicon-based field effect
transistors which host two-dimensional metals4, and certain rare earth
compounds at the threshold of magnetism5-8. The origin of the non-Fermi liquid
behaviour in all of these systems remains controversial. Here we report that an
entirely different and exceedingly simple class of materials - doped small gap
semiconductors near a metal-insulator transition - can also display a non-Fermi
liquid state. Remarkably, a modest magnetic field functions as a switch which
restores the ordinary disordered Fermi liquid. Our data suggest that we have
finally found a physical realization of the only mathematically rigourous route
to a non-Fermi liquid, namely the 'undercompensated Kondo effect', where there
are too few mobile electrons to compensate for the spins of unpaired electrons
localized on impurity atoms9-12.Comment: 17 pages 4 figures supplemental information included with 2 figure
High pressure insulator-metal transition in SmB6
We report the temperature and pressure dependence of the electrical resistivity and Hall constant of single crystal SmB6 for temperatures ranging from 1.2 K to room temperature, and pressures from 1 bar to 80 kbar. Our results indicate that at low pressures SmB6 is an insulator, but undergoes a sudden transition to metallic behavior at a pressure of 50 kbar.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31646/1/0000580.pd
Surface-dominated conduction up to 240 K in the Kondo insulator SmB6 under strain
SmB6 is a strongly correlated mixed-valence Kondo insulator with a newly discovered surface state, proposed to be of non-trivial topological origin. However, the surface state dominates electrical conduction only below T∗ ≈ 4 K (ref. ), limiting its scientific investigation and device application. Here, we report the enhancement of T∗ in SmB6 under the application of tensile strain. With 0.7% tensile strain we report surface-dominated conduction at up to a temperature of 240 K, persisting even after the strain has been removed. This can be explained in the framework of strain-tuned temporal and spatial fluctuations of f-electron configurations, which might be generally applied to other mixed-valence materials. We note that this amount of strain can be induced in epitaxial SmB6 films via substrate in potential device applications
Caractères anatomiques du Discocoffea lasiodelphis Aug. Chevalier.
Beille L. Caractères anatomiques du Discocoffea lasiodelphis Aug. Chevalier.. In: Revue de botanique appliquée et d'agriculture coloniale, 16ᵉ année, bulletin n°179, juillet 1936. pp. 542-546
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