Inducing half metallicity with alloying in Heusler Compound CoFeMnSb.

First principles studies were performed in order to find out the possibility of inducing half-metallicity in Heusler Compound CoFeMnSb, by means of alloying it with 3d-transition metal elements. Proper alloying element is selected through the calculations of formation energies. These calculations were tested with different concentrations of alloying elements at different atomic sites. Among the selected transition metal elements Sc and Ti are proposed to be excellent alloying elements, particularly at Mn site. By using these alloying elements complete half metallic behaviour is obtained in [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and CoFeTiSb alloys. Shifting of Co-Fe d-states towards lower energy region leads to zero density of states at Fermi level for the spin minority channel. Alloying effects on the electronic structure and magnetization are discussed in details. Thermodynamical stability of these new alloys is a major part of this study. The Curie temperatures of [Formula: see text] and [Formula: see text] were found to be 324.5 K and 682 K; respectively, showing good candidature for spintronics applications. For understanding the bonding nature of the constituent atom of CoFeMnSb, crystal orbital Hamiltonian populations have been analysed.

Enhanced superconductivity in SnSb under pressure: a first principles study.

First principles electronic structure calculations reveal both SnP and SnSb to be stable in the NaCl structure. In SnSb, a first order phase transition from NaCl to CsCl type structure is observed at around 13 GPa, which is also confirmed from enthalpy calculations and agrees well with experimental and other theoretical reports. Calculations of the phonon spectra, and hence the electron-phonon coupling [Formula: see text] and superconducting transition temperature T c, were performed at zero pressure for both the compounds, and at high pressure for SnSb. These calculations report [Formula: see text] of [Formula: see text] K and [Formula: see text] K for SnP and SnSb respectively, in the NaCl structure-in good agreement with experiment-whilst at the transition pressure, in the CsCl structure, a drastically increased value of T c around [Formula: see text] K ([Formula: see text] K at 20 GPa) is found for SnSb, together with a dramatic increase in the electronic density of states at this pressure. The lowest energy acoustic phonon branches in each structure also demonstrate some softening effects, which are well addressed in this work.

Predicted superconductivity of Ni2VAl and pressure dependence of superconductivity in Ni2NbX (X = Al, Ga and Sn) and Ni2VAl.

A first-principles study of the electronic and superconducting properties of the Ni2VAl Heusler compound is presented. The electron-phonon coupling constant of λ(ep)=0.68 is obtained, which leads to a superconducting transition temperature of Tc = ~ 4K (assuming a Coulomb pseudopotential µ(*)=0.13), which is a relatively high transition temperature for Ni based Heusler alloys. The electronic density of states reveals a significant hybridization between Ni-eg and V-t(2g) states around the Fermi level. The Fermi surface, consisting of two electron pockets around the X-points of the Brillouin zone, exhibits nesting and leads to a Kohn anomaly of the phonon dispersion relation for the transverse acoustic mode TA2 along the (1, 1, 0) direction, which is furthermore found to soften with pressure. As a consequence, T(c) and λ(ep) vary non-monotonically under pressure. The calculations are compared to similar calculations performed for the Ni2NbX (X = Al, Ga and Sn) Heusler alloys, which experimentally have been identified as superconductors. The experimental trend in T(c) is well reproduced, and reasonable quantitative agreement is obtained. The calculated T(c) of Ni2VAl is larger than either calculated or observed T(c)s of any of the Nb compounds. The Fermi surfaces of Ni2NbAl and Ni2NbGa consist of only a single electron pocket around the X point, however under compression a second electron pocket similar to that of Ni2VAl emerges Ni2NbAl and the T(c) increases non-monotonically in all the compounds. Fermi surface nesting and associated Kohn anomalies are a common feature of all four compounds, albeit weakest in Ni2VAl.