Phase diagrams for films of two-component magnetic alloys

Phase diagrams for diluted bulk magnetic alloys and two-component magnetic films are investigated. On the basis of the Ising model for layered structures, we calculate the transition temperature as a function of the relative concentration χ by means of the variational cumulant expansion. Both the ferromagnetic and antiferromagnetic interactions are considered and the exchange coupling constants between different atoms are treated as adjustable parameters. Experimental phase diagrams in the T_c-χ plane for both La₂Cu_1-χZn_χO₄ and Sm₂Fe_14-χCo_χSi₂ are qualitatively accounted for, and phase diagrams for a randomly mixed two-component thin film of magnetic alloys are predicted.