841 research outputs found
Stability of Weyl points in magnetic half-metallic Heusler compounds
We employ {\it ab-initio} fully-relativistic electronic structure
calculations to study the stability of the Weyl points in the momentum space
within the class of the half-metallic ferromagnetic full Heusler materials, by
focusing on CoTiAl as a well-established prototype compound. Here we show
that both the number of the Weyl points together with their -space
coordinates can be controlled by the orientation of the magnetization. This
alternative degree of freedom, which is absent in other topological materials
(e.g. in Weyl semimetals), introduces novel functionalities, specific for the
class of half-metallic ferromagnets. Of special interest are Weyl points which
are preserved irrespectively of any arbitrary rotation of the magnetization
axis
Heusler 4.0: Tunable Materials
Heusler compounds are a large family of binary, ternary and quaternary
compounds that exhibit a wide range of properties of both fundamental and
potential technological interest. The extensive tunability of the Heusler
compounds through chemical substitutions and structural motifs makes the family
especially interesting. In this article we highlight recent major developments
in the field of Heusler compounds and put these in the historical context. The
evolution of the Heusler compounds can be described by four major periods of
research. In the latest period, Heusler 4.0 has led to the observation of a
variety of properties derived from topology that includes: topological metals
with Weyl and Dirac points; a variety of non-collinear spin textures including
the very recent observation of skyrmions at room temperature; and giant
anomalous Hall effects in antiferromagnetic Heuslers with triangular magnetic
structures. Here we give a comprehensive overview of these major achievements
and set research into Heusler materials within the context of recent emerging
trends in condensed matter physics
Premartensite to martensite transition and its implications on the origin of modulation in Ni2MnGa ferromagnetic shape memory alloy
We present here results of temperature dependent high resolution synchrotron
x-ray powder diffraction study of sequence of phase transitions in Ni2MnGa. Our
results show that the incommensurate martensite phase results from the
incommensurate premartensite phase, and not from the austenite phase assumed in
the adaptive phase model. The premartensite phase transforms to the martensite
phase through a first order phase transition with coexistence of the two phases
in a broad temperature interval (~40K), discontinuous change in the unit cell
volume as also in the modulation wave vector across the transition temperature
and considerable thermal hysteresis in the characteristic transition
temperatures. The temperature variation of the modulation wave vector q shows
smooth analytic behaviour with no evidence for any devilish plateau
corresponding to an intermediate or ground state commensurate lock-in phases.
The existence of the incommensurate 7M like modulated structure down to 5K
suggests that the incommensurate 7M like modulation is the ground state of
Ni2MnGa and not the Bain distorted tetragonal L10 phase or any other lock-in
phase with a commensurate modulation. These findings can be explained within
the framework of the soft phonon model
Structural, magnetic, and transport properties of CoFeSi Heusler films
We report the deposition of thin CoFeSi films by RF magnetron sputtering.
Epitaxial (100)-oriented and L2 ordered growth is observed for films grown
on MgO(100) substrates. (110)-oriented films on AlO(110) show several
epitaxial domains in the film plane. Investigation of the magnetic properties
reveals a saturation magnetization of 5.0 at low temperatures. The
temperature dependence of the resistivity exhibits a crossover
from a T^3.5 law at T<50K to a T^1.65 behaviour at elevated temperatures.
shows a small anisotropic magnetoresistive effect. A weak
dependence of the normal Hall effect on the external magnetic field indicates
the compensation of electron and hole like contributions at the Fermi surface.Comment: 10 pages, 9 figures to be published in J. Phys. D: Appl. Phy
Observation of Landau quantization and standing waves in HfSiS
Recently, HfSiS was found to be a new type of Dirac semimetal with a line of
Dirac nodes in the band structure. Meanwhile, Rashba-split surface states are
also pronounced in this compound. Here we report a systematic study of HfSiS by
scanning tunneling microscopy/spectroscopy at low temperature and high magnetic
field. The Rashba-split surface states are characterized by measuring Landau
quantization and standing waves, which reveal a quasi-linear dispersive band
structure. First-principles calculations based on density-functional theory are
conducted and compared with the experimental results. Based on these
investigations, the properties of the Rashba-split surface states and their
interplay with defects and collective modes are discussed.Comment: 6 pages, 5 figure
Electronic Structure, Localization and Spin-State Transition in Cu-substituted FeSe: FeCuSe
We report density functional studies of the FeCuSe alloy done
using supercell and coherent potential approximation methods. Magnetic behavior
was investigated using the disordered local moment approach. We find that Cu
occurs in a nominal configuration and is highly disruptive to the
electronic structure of the Fe sheets. This would be consistent with a metal
insulator transition due to Anderson localization. We further find a strong
cross over from a weak moment itinerant system to a local moment magnet at . We associate this with the experimentally observed jump near
this concentration. Our results are consistent with the characterization of
this concentration dependent jump as a transition to a spin-glass
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