Investigation of structural, elastic, electronic, and magnetic proprieties for X2LuSb (X = Mn and Ir) full-Heusler alloys

Review of high-throughput computational design of Heusler alloys

The linear wave augmented plane waves method at full potential using the functional density theory and applying the approximation methods “GGA-PBE, PBE-sol, mBJ and GGA + U” has been used to investigate the electronic, thermoelectric, magnetic and transport properties of Full-Heusler F e 2 M n S i . The optimized and the most stable crystal structure at equilibrium is face-centered cubic with space group and lattice parameters a = 5.591 A. The half metallic character is observed with an indirect band gap. To determine the stability of this material, the elastic parameters have been computed. Moreover, the Seebeck coefficients and the electrical conductivity have been obtained. It is found that the spin polarization (SP) reaches 100% for F e 2 M n S i due to its half metallic state.

Structural, electronic, magnetic and thermoelectric properties of Full-Heusler Fe2MnSi: Ab initio calculations

The half metallic feature at high temperature of the novel half-Heusler alloys and their [100] oriented layered superlattices: A DFT investigations

The advent of spin transfer torque effect accommodates site-specific switching of magnetic nanostructures by current alone without magnetic field. However, the critical current density required for usual spin torque switching remains stubbornly high around 10(6)-10(7) A cm(-2). It would be fundamentally transformative if an electric field through a voltage could assist or accomplish the switching of ferromagnets. Here we report electric-field-assisted reversible switching in CoFeB/MgO/CoFeB magnetic tunnel junctions with interfacial perpendicular magnetic anisotropy, where the coercivity, the magnetic configuration and the tunnelling magnetoresistance can be manipulated by voltage pulses associated with much smaller current densities. These results represent a crucial step towards ultralow energy switching in magnetic tunnel junctions, and open a new avenue for exploring other voltage-controlled spintronic devices.

http://absimage.aps.org/image/MAR12/MWS_MAR12-2011-001966.pdf

Electric field assisted switching in magnetic tunnel junctions

Study of half-metallicity has been performed in a new series of Mn2ScZ (Z = Si, Ge and Sn) full Heusler alloys using density functional theory with the calculation and implementation of a Hubbard correction term (U). Volume optimization in magnetic and non-magnetic phases for both the Cu2MnAl and Hg2CuTi type structures was done to predict the stable ground state configuration. The stability was determined by calculating their formation energy as well as from elastic constants under ambient conditions. A half-metal is predicted for Mn2ScSi and Mn2ScGe with a narrow band gap in the minority spin whereas Mn2ScSn shows a metallic nature. The magnetic moments of Mn and Sc are coupled in opposite directions with different strengths indicating that the ferrimagnetic order and the total magnetic moment per formula unit for half-metals follows the Slater Pauling rule. And a strong effect was shown by the size of the Z element in the electronic and magnetic properties.

/pdf/half-metallicity-in-new-heusler-alloys-mn2scz-z-si-ge-sn-1zip0qfolc.pdf

Half-metallicity in new Heusler alloys Mn2ScZ (Z = Si, Ge, Sn)

A theoretical investigation of electronic and magnetic properties has been performed on the new members of Heusler alloys M2NiZ (M = Sc, Ti, and V; Z = Tl and Pb) that crystallize in an inverse Heusler XA structure. The overall electronic properties and magnetic moments are predominated by M atoms, where the total magnetic moment varies linearly with the number of valence electrons, following the Slater–Pauling rule with ferro- or ferri-magnetic ground states. Their Curie temperatures are well above the room temperature and are comparable to analogous compounds. Among the sample alloys, Sc2NiTl, Ti2NiTl, and Ti2NiPb are half-metals, whereas V2NiTl has a nearly half-metallic profile that can be tuned into novel half-metal under uniform strain. Their thermodynamic, mechanical, and dynamical stabilities are also verified from their formation energy, elastic constants, and phonon spectra, respectively. A strong correlation between the directional elastic sound velocities and spatial dependence of elastic moduli is also observed. The evaluated Poisson's ratio from elastic constants and charge density plots predicts the partial ionic nature of Ti2NiTl and Ti2NiPb and the covalent nature of Sc2NiTl and V2NiTl. The optical phonon modes are found to be both Raman and infrared active, whereas the reststrahlen band is observed in the far-infrared region.

Mechanical stability and origin of half-metallicity of new M2NiZ (M = Sc, Ti, and V; Z = Tl and Pb) Heusler alloys

The electronic and magnetic properties of Mn2ZnSi(1−x)Gex (x = 0.0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, and 1.0) inverse Heusler alloys and Mn2ZnSi/Mn2ZnGe superlattice have been investigated using first-principles calculations. All these alloys are stable in the fcc magnetic phase and satisfies the mechanical and thermal stability conditions as determined from the elastic constants and negative formation energy. The spin-polarized electronic band structures and the density of states indicate half-metallicity with 100% spin polarization at the Fermi energy level for x = 0.0, 0.125, 0.25, 0.50, and 1.0, with the integral values of the total magnetic moments per formula unit at their equilibrium lattice constants, following the Slater–Pauling rule. The electronic properties and the magnetic moments are mostly contributed by two Mn atoms and are coupled anti-parallel to each other, making them ferrimagnetic in nature. The presence of the half-metallic bandgap with an antiparallel alignment of Mn atoms makes these Heusler alloys a potential candidate for spintronic applications.

/pdf/study-of-half-metallicity-structural-and-mechanical-16vkr5ecso.pdf

Study of half metallicity, structural and mechanical properties in inverse Heusler alloy Mn2ZnSi(1−x)Gex and a superlattice

A semimetallic type of electronic profile has been predicted for RFe4Sb12 (R = Pr, Nd) from a first-principles investigation, where the presence of a small energy bandgap above the Fermi energy level (EF) is a key feature. The EF lies at the top of the valence band and it is crossed by a single band more than twice, which improves the band concentration and electronic specific heat as reflected by the high Seebeck coefficient. The doping of a heavy lanthanide atom at the center of the cage formed by pnictogen atoms has a significant effect on the electronic structure that enhances the Seebeck coefficient and the thermoelectric power factor. The heavy atom at the center also dampens the lattice vibration and lowers the lattice thermal conductivity. The Nd-doped system shows an enhanced Seebeck coefficient with the highest power factor among the sample alloys. Moreover, due to significant reduction in the lattice thermal conductivity from 2.46 W/m K to 0.54 W/m K, a maximum ZT value of ∼1.11 at 800 K has been observed for an Nd-doped system. The covalent nature of PrFe4Sb12, Pr-doped NdFe4Sb12, and Nd-doped PrFe4Sb12 and the ionic nature of NdFe4Sb12 have been confirmed, where Pr-doped NdFe4Sb12 is the stiffest and a highly rigid material with strong bonding forces among the constituent atoms. The results presented in this manuscript open the possibilities for further exploration of center atom-doped filled skutterudites with improved Seebeck coefficient and reduced lattice thermal conductivity, which are promising materials for thermoelectric applications

Enhanced electronic and thermoelectric properties of p-type doped filled skutterudites RFe4Sb12 (R = Pr, Nd)

A theoretical study of electronic, mechanical and dynamical properties of RuCrP alloy has been performed using the density functional theory based on the plane-wave basis set and pseudopotential method. The structural optimization plot confirms that the ferromagnetic phase is energetically more favorable among the other phases. The stability of the sample alloy was determined by calculating their cohesive energy as well as from the elastic constants. The elastic parameters displayed the mechanically anisotropic and ductile nature of the sample alloy. We also investigated the phonon dispersion curve and found that the phonon frequency modes were positive, indicating the dynamical stability of the compound. The observed optical phonon modes were a mixture of Raman and infrared active. Generalized gradient approximation (GGA) and GGA+U (U = Hubbard parameter) methods were adopted for calculation of actual ground state properties. In both the schemes, the sample material revealed its Half-metallic behavior. Moreover, the charge density plot predicted the covalent character of the sample alloy. As the Curie temperature ( T C ) of the studied material was found to be higher than room temperature; the material is suitable for spintronic applications.

M. Ram

Papers

Half-metallicity in new Heusler alloys Mn2ScZ (Z = Si, Ge, Sn)

Mechanical stability and origin of half-metallicity of new M2NiZ (M = Sc, Ti, and V; Z = Tl and Pb) Heusler alloys

Study of half metallicity, structural and mechanical properties in inverse Heusler alloy Mn2ZnSi(1−x)Gex and a superlattice

Enhanced electronic and thermoelectric properties of p-type doped filled skutterudites RFe4Sb12 (R = Pr, Nd)

Study of lattice dynamic, electronic and mechanical properties of Half-Heusler RuCrP alloy