Magnetic and structural properties of Co-Ni-Z (Z = Al, Ga, In, Sn) Heusler alloys: Effect of structural motives and chemical disorder

Ground state properties of Ni-excess Co(2)Ni(1+x)Z(1-x)(Z = Al, Ga, In, Sn) full Heusler alloys are investigated by ab initio calculations. We consider the effect of different structural motives and chemical disorder on structural stability and magnetic characteristics of these alloys. Co-Ni-(In, Sn) are found to be unstable with respect to decomposition into pure bulk elements. Co2Ni(Al, Ga) are stable, however, introducing the Ni excess destabilizes these alloys making off-stoichiometric Co2Ni1+xAl and Co2Ni1+xGa1-x unstable at x > 0.5 and x > 0.25, respectively. Saturation magnetization M-s of Co2Ni(Al, Ga) is of the same order like other Co2Ni-based Heusler alloys. Our study showed that an effective way to increase M-s is the introducing of chemical disorder. For stable compounds in which a tetragonal structure with alternating planes of Co and Ni exists, we calculate the magnetocrystalline anisotropy energy (MAE) given large values about -2 MJ/m(3) with in-plane favorable spin configuration. The deviation from stoichiometry reduces the MAE by a factor of two.

Automated summary

The ground state properties of Ni-excess Co(2)Ni(1+x)Z(1-x)(Z = Al, Ga, In, Sn) full Heusler alloys were investigated using ab initio calculations. The effect of different structural motives and chemical disorder on the stability and magnetic characteristics of these alloys was considered. It was found that introducing chemical disorder can effectively increase the saturation magnetization. The deviation from stoichiometry affects the stability of the alloys and reduces the magnetocrystalline anisotropy energy.