524 research outputs found
Half-metallic ferromagnets: From band structure to many-body effects
A review of new developments in theoretical and experimental electronic
structure investigations of half-metallic ferromagnets (HMF) is presented.
Being semiconductors for one spin projection and metals for another ones, these
substances are promising magnetic materials for applications in spintronics
(i.e., spin-dependent electronics). Classification of HMF by the peculiarities
of their electronic structure and chemical bonding is discussed. Effects of
electron-magnon interaction in HMF and their manifestations in magnetic,
spectral, thermodynamic, and transport properties are considered. Especial
attention is paid to appearance of non-quasiparticle states in the energy gap,
which provide an instructive example of essentially many-body features in the
electronic structure. State-of-art electronic calculations for correlated
-systems is discussed, and results for specific HMF (Heusler alloys,
zinc-blende structure compounds, CrO FeO) are reviewed.Comment: to be published in Reviews of Modern Physics, vol 80, issue
First-principles investigation of competing magnetic interactions in (Mn,Fe)RuSn Heusler solid solutions
Many Heusler compounds possess magnetic properties well-suited for
applications as spintronic materials. The pseudo-binary
MnFeRuSn, formed as a solid solution of two full Heuslers,
has recently been shown to exhibit exchange hardening suggestive of two
magnetic phases, despite existing as a \textit{single} chemical phase. We have
performed a first-principles study of the chemical and magnetic degrees of
freedom in the MnFeRuSn pseudo-binary to determine the origin
of the unique magnetic behavior responsible for exchange hardening within a
single phase. We find a transition from antiferromagnetic (AFM) to
ferromagnetic (FM) behavior upon replacement of Mn with Fe, consistent with
experimental results. The lowest energy orderings in MnFeRuSn
consist of chemically- and magnetically-uniform (111) planes, with Fe-rich
regions preferring FM ordering and Mn-rich regions preferring AFM ordering,
independent of the overall composition. Analysis of the electronic structure
suggests that the magnetic behavior of this alloy arises from a competition
between AFM-favoring Sn-mediated superexchange and FM-favoring RKKY exchange
mediated by spin-polarized conduction electrons. Changes in valency upon
replacement of Mn with Fe shifts the balance from superexchange-dominated
interactions to RKKY-dominated interactions.Comment: 14 pages, 9 figure
Half-metallicity and Slater-Pauling behavior in the ferromagnetic Heusler alloys
Introductory chapter for the book "Halfmetallic Alloys - Fundamentals and
Applications" to be published in the series Springer Lecture Notes on Physics,
P. H. Dederichs and I. Galanakis (eds). It contains a review of the theoretical
work on the half-metallic Heusler alloys.Comment: Introductory chapter for the book "Halfmetallic Alloys - Fundamentals
and Applications" to be published in the series Springer Lecture Notes on
Physics, P. H. Dederichs and I. Galanakis (eds
Electronic structure and magnetism in doped semiconducting half-Heusler compounds
We have studied in details the electronic structure and magnetism in M (Mn
and Cr) doped semiconducting half-Heusler compounds FeVSb, CoTiSb and NiTiSn
(XMYZ) in a wide concentration range using local-spin density
functional method in the framework of tight-binding linearized muffin tin
orbital method(TB-LMTO) and supercell approach. Our calculations indicate that
some of these compounds are not only ferromagnetic but also half-metallic and
may be useful for spintronics applications. The electronic structure of the
doped systems is analyzed with the aid of a simple model where we have
considered the interaction between the dopant transition metal (M) and the
valence band X-Z hybrid. We have shown that the strong X-d - M-d interaction
places the M-d states close to the Fermi level with the M-t states lying
higher in energy in comparison to the M-e states. Depending on the number
of available d-electrons, ferromagnetism is realized provided the d-manifold is
partially occupied. The tendencies toward ferromagnetic(FM) or
antiferromagnetic(AFM) behavior are discussed within Anderson-Hasegawa models
of super-exchange and double-exchange. In our calculations for Mn doped NiTiSn,
the strong preference for FM over AFM ordering suggests a possible high Curie
temperature for these systems.Comment: 14 pages, 6 figure
First-principles calculations to investigate the structural, electronic, elastic, vibrational and thermodynamic properties of the full-Heusler alloys X2ScGa (X = Ir and Rh)
This study has investigated ab initio pseudopotential calculations on the structural, electronic, elastic, vibrational and thermodynamic properties of the full-Heusler X2ScGa (X = Ir and Rh) alloys. The calculations have taken place under consideration of the generalized gradient approximation (GGA) of the density functional theory (DFT) with using the plane-wave ab initio pseudopotential method. According to the calculations, the major contribution to electronic states at the Fermi energy has been achieved by d orbitals, revealing a more active role for transition metals Ir (Rh) and Sc atoms. The reckonings point out that the Ir2ScGa and Rh2ScGa have metallic behavior at the equilibrium lattice constant with the density of states (DOS) at the Fermi level (N (EF)) of 1.412 states/eV and 1.821 states/eV, respectively. The results of the elastic constants showed that these compounds met the criteria for Born mechanical stability. It was also observed that they have a ductile structure and exhibit anisotropic behavior according to Pugh criteria. Besides, the full phonon spectra and their projected partial density of states of the alloys have been analyzed with the first-principle linear-response approach of the density-functional perturbation theory. All the alloys behaved dynamically stable in the L21 phase. Furthermore, internal free energy, entropy, specific heat capacity at constant volume and vibrational free energy changes of Ir2ScGa and Rh2ScGa alloys were analyzed and discussed between the temperature range of 0–800 K using the quasi harmonic approximation. According to the results, these alloys are potential candidate for industrial use. © 2020 Elsevier Lt
Optical and magneto-optical properties of ferromagnetic full-Heusler films: experiments and first-principles calculations
We report a joint theoretical and experimental study focused on understanding
the optical and magneto-optical properties of Co-based full-Heusler compounds.
We show that magneto-optical spectra calculated within ab-initio density
functional theory are able to uniquely identify the features of the
experimental spectra in terms of spin resolved electronic transitions. As
expected for 3d-based magnets, we find that the largest Kerr rotation for these
alloys is of the order of 0.3o in polar geometry. In addition, we demonstrate
that (i) multilayered structures have to be carefully handled in the
theoretical calculations in order to improve the agreement with experiments,
and (ii) combined theoretical and experimental investigations constitute a
powerful approach to designing new materials for magneto-optical and
spin-related applicationsComment: 20 pages, including 6 figures and 1 table. 40 refs. To be published
in Phys. Rev.
First-Principal Investigations of the Electronic, Magnetic, and Thermoelectric Properties of CrTiRhAl Quaternary Heusler Alloy
Density functional theory calculations are performed to investigate the electrical electronic, magnetic, and thermoelectric properties of CrTiRhAl quaternary Heusler alloy (QHA). The type-I atomic configuration is found to be the most stable structure of this alloy. The CrTiRhAl QHA exhibits a half-metallic ferromagnetic structure with a narrow band gap at one spin channel (semiconductor), and a metallic behavior at the other spin channel. This corresponds to a 100% spin-polarization, making it ideal for potential spintronic applications. Applying the semi-classical Boltzmann theory, the Seebeck coefficient, electrical conductivity, and electronic thermal conductivity of CrTiRhAl alloy were calculated. The predicted figure of merit (ZT) was found to be low (0.4 at 300K), which is not promising for thermoelectric applications. Keywords: Quaternary Heusler alloy, magnetic properties, lattice thermal conductivity, thermoelectric properties
First-Principal Investigations of the Electronic, Magnetic, and Thermoelectric Properties of CrTiRhAl Quaternary Heusler Alloy
Density functional theory calculations are performed to investigate the electrical electronic, magnetic, and thermoelectric properties of CrTiRhAl quaternary Heusler alloy (QHA). The type-I atomic configuration is found to be the most stable structure of this alloy. The CrTiRhAl QHA exhibits a half-metallic ferromagnetic structure with a narrow band gap at one spin channel (semiconductor), and a metallic behavior at the other spin channel. This corresponds to a 100% spin-polarization, making it ideal for potential spintronic applications. Applying the semi-classical Boltzmann theory, the Seebeck coefficient, electrical conductivity, and electronic thermal conductivity of CrTiRhAl alloy were calculated. The predicted figure of merit (ZT) was found to be low (0.4 at 300K), which is not promising for thermoelectric applications. Keywords: Quaternary Heusler alloy, magnetic properties, lattice thermal conductivity, thermoelectric properties
High-throughput design of all-d-metal Heusler alloys for magnetocaloric applications
Due to their versatile composition and customizable properties, ABC
Heusler alloys have found applications in magnetic refrigeration, magnetic
shape memory effects, permanent magnets, and spintronic devices. The discovery
of all--metal Heusler alloys with improved mechanical properties compared to
those containing main group elements, presents an opportunity to engineer
Heuslers alloys for energy-related applications. Using high-throughput density
functional theory calculations, we screened magnetic all--metal Heusler
compounds and identified 686 (meta)stable compounds. Our detailed analysis
revealed that the inverse Heusler structure is preferred when the
electronegativity difference between the A and B/C atoms is small, contrary to
conventional Heusler alloys. Additionally, our calculations of Pugh ratios and
Cauchy pressures demonstrated that ductile and metallic bonding are widespread
in all--metal Heuslers, supporting their enhanced mechanical behaviour. We
identified 49 compounds with a double-well energy surface based on Bain path
calculations and magnetic ground states, indicating their potential as
candidates for magnetocaloric and shape memory applications. Furthermore, by
calculating the free energies, we propose that 11 compounds exhibit structural
phase transitions, and propose isostructural substitution to enhance the
magnetocaloric effect
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