Phase Diagrams and Multicritical Points in Randomly Mixed Alloys

Abstract

The Landau-Ginzburg-Wilson model associated with the random alloy ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{\mathrm{Cl}}_2$ is analyzed. It is observed that the model includes a coupling term which has thus far been overlooked. Renormalization-group calculations in $d=4-\epsilon$ dimensions suggest that the multicritical behavior of this system is not associated with the "decoupled" fixed point found in previous theories. This prediction is consistent with recent experiments. A microscopic mechanism which generates this term is considered. It is suggested that similar terms may appear in other quenched alloys.