Phase diagrams and multicritical points in randomly mixed alloys

The Landau-Ginzburg-Wilson model associated with the random alloy Fe1-xCoxCl2 is analyzed. It is observed that the model includes a coupling term which has thus far been overlooked. Renormalization-group calculations in d=4 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. © 1981 The American Physical Society.