Atomic disorder in Heusler alloy Cr₂CoGa

Heusler alloy Cr₂CoGa with 24 valence electrons is a promising candidate for half-metallic completely compensated ferrimagnets. Its electronic structure and atomic disorder have been investigated by using a KKR–CPA method. The equilibrium lattice constant is 5.88 Å and the total moment is as small as 0.09 μ_B. This near zero moment is mainly determined by the antiparallel aligned Cr (A) and Cr (B) spin moments, which are −2.16 μ_B and 2.17 μ_B, respectively and compensate each other. The calculated spin polarization ratio is as high as 95%. Three kinds of atomic disorder have been considered in Cr₂CoGa: Cr (B)-Co, Cr (A)-Co and Cr (B)-Ga. Among them, Cr (A)-Co and especially Cr (B)-Co disorder raise the total energy obviously. While Cr (B)-Ga disorder decreases the total energy by ~0.14 eV. So Cr (B)-Ga disorder is more energetically favored in the sample. The influence of Cr (B)-Ga disorder on the magnetic moment and electronic structure is small. The total moment only increases slightly to 0.16 μ_B. The influence of Cr (A)-Co disorder on the magnetic properties is also not obvious. Whereas Cr (B)-Co disorder increases the total moment obviously, which is mainly related to the ferromagnetic coupling between the Cr spin moments at A, C sites.