Enhancement of L21 order and spin-polarization in Co2FeSi thin film by substitution of Fe with Ti

Abstract

We investigated the effect of Ti substitution for Fe in Co2FeSi Heusler alloy (Co2Fe1-xTixSi) on their electronic structure, chemical ordering, and spin-dependent transport properties. First-principles calculations of the density of states (DOS) indicated that the peak just above the Fermi level in the minority-spin DOS (the conduction band edge of half-metallic gap) shifts towards higher energies with increasing Ti, leading to the enhancement in the half-metallic gap and the spin-polarization. We found in epitaxial Co2(Fe1-xTix)Si thin films that the required annealing temperature for long range L21-ordering can be substantially reduced from 650 °C for Co2FeSi to 400 °C for x ≥ 0.2. The enhancement of spin-polarization by the substitution of Fe with Ti was experimentally confirmed from anisotropic magnetoresistance measurements and spin-accumulation signals in non-local spin valve devices with the Co2Fe1-xTixSi films.