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

Abstract 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 a b i n i t i o 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. Co 2 Ni(Al, Ga) are stable, however, introducing the Ni excess destabilizes these alloys making off-stoichiometric Co 2 Ni 1 + x Al 1 − x and Co 2 Ni 1 + x Ga 1 − x unstable at x > 0 . 5 and x > 0 . 25 , respectively. Saturation magnetization  M s of Co 2 Ni(Al, Ga) is of the same order like other Co 2 Ni-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 twice the MAE.