Theoretical, Materials and Condensed Matter Physics

Biography

Biography: Rita John

Abstract

Heusler alloys are intermetallic compounds made up of four interpenetrating fcc sublattices. Some of them have multifunctional nature i.e. a combination of functions (properties) within the same compound, which have technological applications. Co-based Heusler compounds gained considerable attention in the recent past due to their high Curie temperature, high spin polarization and tunable electronic structure with possible applications in spintronics. They have the general composition X2 YZ where X and Y are transition metals and Z is an sp element. Quaternary Heusler alloys (QHA) are formed when one of the X atoms is replaced by a third transition metal. In this study, the structural, electronic, magnetic and transport properties of CoFeNbZ (Z=Al, Si and In) quaternary Heusler compounds are investigated employing the full potential linearized augmented plane wave (FP-LAPW) method implemented in WIEN2k code within the density functional theory prescription. The exchange and correlation effects are treated by using generalized gradient approximation (GGA). From the electronic and magnetic properties, it is found that CoFeNbAl is a half-metal with a spin flip gap of 0.33 eV and satisfies the Mt =Zt –24 Slater Pauling rule. It is known that GGA underestimates the band gaps of semiconductors and insulators. Here, the Tran and Blaha modified Becke Johnson potential (TB-mBJ) is used to obtain accurate band gaps. The spin-flip gap increases to 0.34 eV with the use of TB-mBJ and the nature of gap changes from indirect to direct. The half-metallic gap in CoFeNbAl arises due to the complex hybridization between the d-states of transition metals Co, Fe, and Nb. CoFeNbIn has metallic behavior in both spin channels. CoFeNbSi is a near half-metal with a near integer magnetic moment. The effect of hydrostatic strain on the magnetic and half-metallic properties of CoFeNbAl is determined. The transport coefficients such as the Seebeck coefficient, electrical conductivity, and thermal conductivity are computed in combination with the second principles BoltzTraP code. In the spin-up channel, electrical conductivity decreases as a function of temperature whereas it increases in the spin down the channel for CoFeNbAl. This affirms the metallic behavior in the spin-up channel and the semiconducting behavior in the spin down channel. The high spin polarization and robustness of half-metallicity against hydrostatic strain make CoFeNbAl a potential candidate for spintronic applications.