Formation of a weak ferromagnetic state in Y(Co_1-xAl_x)₂ compounds: a coherent potential approximation study

The band structure of substitutionally disordered Y(Co_1-xAl_x)₂ has been calculated for various concentrations in the range 0⩽x⩽0.25 employing the coherent potential approximation embodied in an all-electron tight-binding linear muffin-tin orbital method. On the basis of the results, we provide a new explanation for the formation of weak ferromagnetic moments in these compounds. The discussion of the non-spin-polarized calculated densities of states is supported by direct evidence of the weak ferromagnetic states for certain lattice constants and Al concentrations. The roles of the disorder and the volume effects are discussed.