Site selectivity and moment distribution in V and Cr substituted CoGa alloys

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Abstract
The substitution of V and Cr for Ga in the equiatomic alloy CoGa results in the appearance of ferromagnetism beyond a critical concentration which appears to be related to an average electron-atom ratio rather than to any obvious feature of the crystallographic ordering. Neutron diffraction results are consistent with a model in which at low concentrations the alloys order with the B2 structure but as the transition metal concentration increases double ordering of the L21 type is observed. Despite the similarity in bulk magnetic properties the moment distribution in the V system appears evenly distributed on the Co sublattice whereas in the Cr system the Cr atoms also possess a moment. These may be involved in the formation of superparamagnetic assemblies which diffuse scattering measurements suggest exist in the Co(GaCr) alloys.