Structural, magnetic, and transport properties of epitaxial thin films of equiatomic quaternary CoFeCrGa Heusler alloy

Abstract

We present the first report on the structural, magnetic, and transport properties of epitaxial thin films of equiatomic quaternary CoFeCrGa, grown on a single crystal MgO(001) substrate. From the structure and surface morphology analyses, we have shown that the films grown are ordered, epitaxial, and homogeneous. Magnetic measurements confirm the soft ferromagnetic nature of the film along the in-plane direction with a coercivity of 4.6 Oe. The resistivity measurements indicate semiconducting nature with a very low temperature coefficient of resistivity (TCR) value, suggesting an almost temperature independent resistivity, similar to other reported spin-gapless semiconductors (SGSs) among the Heusler alloys. A non-saturating, quantum linear magnetoresistance is observed even in high fields of up to 12 kOe, another prerequisite for gapless materials. Hall measurements are also performed, and a detailed analysis has been carried out to estimate the ordinary and anomalous Hall contributions. The conductivity value (σxx) at 300 K is found to be 4280 S cm−1, which is comparable with the other reported SGS materials. We have also studied the effect of L21 and B2 type disorder on the electronic properties based on the first principle calculations and found that the SGS nature in CoFeCrGa is quite robust against the Co–Fe swap disorder (L21 disorder); however, with swap disorder (≥25%) between Cr and Ga sites, the system transits from SGS to half-metallic state. All these results indicate the possibility of spin-gapless semiconducting nature in the CoFeCrGa film, making it highly suitable for spin-based device applications.