First principle studies of the structural properties of Heusler Co-Ni-Sn alloys

The structural and magnetic properties of Heusler alloys Co$_{2}$Ni$_{1+x}$Sn$_{1-x}$ ($x$ = 0, 0.25, 0.5, 0.75, 1) were studied using an ab initio approach. The dependences of the total energy of the crystal structure on the degree of tetragonal distortions are obtained, and the most favorable crystal ordering is revealed. The energy of magnetocrystalline anisotropy is calculated for all considered compositions. It is shown that all compositions with a reverse Heusler structure have an easy-plane anisotropy, whereas in the case of a regular Heusler structure, the type of anisotropy changes from an easy-plane to an easy axis with an increase in the Ni content.The largest value of anisotropy was found for the nonstoichiometric compositions Co$_2$Ni$_{1.5}$Sn$_{0.5}$ and Co$_2$Ni$_{1.75}$Sn$_{0.25}$.