152 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
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
Large zero-field cooled exchange-bias in bulk Mn2PtGa
We report a large exchange-bias (EB) effect after zero-field cooling the new
tetragonal Heusler compound Mn2PtGa from the paramagnetic state. The
first-principle calculation and the magnetic measurements reveal that Mn2PtGa
orders ferrimagnetically with some ferromagnetic (FM) inclusions. We show that
ferrimagnetic (FI) ordering is essential to isothermally induce the exchange
anisotropy needed for the zero-field cooled (ZFC) EB during the virgin
magnetization process. The complex magnetic behavior at low temperatures is
characterized by the coexistence of a field induced irreversible magnetic
behavior and a spin-glass-like phase. The field induced irreversibility
originates from an unusual first-order FI to antiferromagnetic transition,
whereas, the spin-glass like state forms due to the existence of anti-site
disorder intrinsic to the material.Comment: 5 pages, 4 figures, supplementary material included in a separate
file; accepted for publication in PR
Electron correlations in CoMnFeSi Heusler compounds
This study presents the effect of local electronic correlations on the
Heusler compounds CoMnFeSi as a function of the concentration
. The analysis has been performed by means of first-principles
band-structure calculations based on the local approximation to spin-density
functional theory (LSDA). Correlation effects are treated in terms of the
Dynamical Mean-Field Theory (DMFT) and the LSDA+U approach. The formalism is
implemented within the Korringa-Kohn-Rostoker (KKR) Green's function method.
In good agreement with the available experimental data the magnetic and
spectroscopic properties of the compound are explained in terms of strong
electronic correlations. In addition the correlation effects have been analysed
separately with respect to their static or dynamical origin. To achieve a
quantitative description of the electronic structure of
CoMnFeSi both static and dynamic correlations must be treated
on equal footing.Comment: 12 pages, 5 figure
Robust Bain distortion in the premartensite phase of platinum substituted Ni2MnGa magnetic shape memory alloy
The premartensite phase of shape memory and magnetic shape memory alloys
(MSMAs) is believed to be a precursor state of the martensite phase with
preserved austenite phase symmetry. The thermodynamic stability of the
premartensite phase and its relation to the martensitic phase is still an
unresolved issue, even though it is critical to the understanding of the
functional properties of MSMAs. We present here unambiguous evidence for
macroscopic symmetry breaking leading to robust Bain distortion in the
premartensite phase of 10% Pt substituted Ni2MnGa. We show that the robust Bain
distorted premartensite (T2) phase results from another premartensite (T1)
phase with preserved cubic-like symmetry through an isostructural phase
transition. The T2 phase finally transforms to the martensite phase with
additional Bain distortion on further cooling. Our results demonstrate that the
premartensite phase should not be considered as a precursor state with the
preserved symmetry of the cubic austenite phase
New iron-based Heusler compounds Fe2YZ: Comparison with theoretical predictions of the crystal structure and magnetic properties
The present work reports on the new soft ferromagnetic Heusler phases
Fe2NiGe, Fe2CuGa, and Fe2CuAl, which in previous theoretical studies have been
predicted to exist in a tetragonal regular Heusler structure. Together with the
known phases Fe2CoGe and Fe2NiGa these materials have been synthesized and
characterized by powder XRD, 57 Fe M\"ossbauer spectroscopy, SQUID and EDX
measurements. In particular M\"ossbauer spectroscopy was used to monitor the
degree of local atomic order/disorder and to estimate magnetic moments at the
Fe sites from the hyperfine fields. It is shown that in contrast to the
previous predictions all the materials except Fe2NiGa basically adopt the
inverse cubic Heusler (X-) structure with differing degrees of disorder. The
disorder is more enhanced in case of Fe2NiGa, which was predicted as an inverse
Heusler phase. The experimental data are compared with results from ab-inito
electronic structure calculations on LDA level incorporating the effects of
atomic disorder by using the coherent potential approximation (CPA). A good
agreement between calculated and experimental magnetic moments is found for the
cubic inverse Heusler phases. Model calculations on various atomic
configurations demonstrate that antisite disorder tends to enhance the
stability of the X-structure. Given the fundamental scientific and
technological importance of tetragonal Heusler phases the present results call
for further investigations to unravel the factors stabilizing tetragonal
Heusler materials
Large Noncollinearity and Spin Reorientation in the Novel Mn2RhSn Heusler Magnet
Noncollinear magnets provide essential ingredients for the next generation
memory technology. It is a new prospect for the Heusler materials, already well
known due to the diverse range of other fundamental characteristics. Here, we
present a combined experimental and theoretical study of novel noncollinear
tetragonal Mn2RhSn Heusler material exhibiting unusually strong canting of its
magnetic sublattices. It undergoes a spin-reorientation transition, induced by
a temperature change and suppressed by an external magnetic field. Because of
the presence of Dzyaloshinskii-Moriya exchange and magnetic anisotropy, Mn2RhSn
is suggested to be a promising candidate for realizing the Skyrmion state in
the Heusler family
Monitoring surface resonances on Co2MnSi(100) by spin-resolved photoelectron spectroscopy
The magnitude of the spin polarization at the Fermi level of ferromagnetic
materials at room temperature is a key property for spintronics. Investigating
the Heusler compound CoMnSi a value of 93 for the spin polarization has
been observed at room temperature, where the high spin polarization is related
to a stable surface resonance in the majority band extending deep into the
bulk. In particular, we identified in our spectroscopical analysis that this
surface resonance is embedded in the bulk continuum with a strong coupling to
the majority bulk states. The resonance behaves very bulk-like, as it extends
over the first six atomic layers of the corresponding (001)-surface. Our study
includes experimental investigations, where the bulk electronic structure as
well as surface-related features have been investigated using spin-resolved
photoelectron spectroscopy (SR-UPS) and for a larger probing depth
spin-integrated high energy x-ray photoemission spectroscopy (HAXPES). The
results are interpreted in comparison with first-principles band structure and
photoemission calculations which consider all relativistic, surface and
high-energy effects properly.Comment: 9 pages, 8 figures, Heusler alloy, electronic structure and
photoemissio
Orbital magnetism in transition-metal systems: The role of local correlation effects
The influence of correlation effects on the orbital moments for transition
metals and their alloys is studied by first-principle relativistic Density
Functional Theory in combination with the Dynamical Mean-Field Theory. In
contrast to the previous studies based on the orbital polarization corrections
we obtain an improved description of the orbital moments for wide range of
studied systems as bulk Fe, Co and Ni, Fe-Co disordered alloys and 3
impurities in Au. The proposed scheme can give simultaneously a correct
dynamical description of the spectral function as well as static magnetic
properties of correlated disordered metals.Comment: EPL accepte
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