Superexchange induced canted ferromagnetism in dilute magnets

Abstract

We argue, in contrast to recent studies, that the antiferromagnetic superexchange coupling between nearest neighbor spins does not fully destroy the ferromagnetism in dilute magnets with long-ranged ferromagnetic couplings. Above a critical coupling, we find a canted ferromagnetic phase with unsaturated moment. We have calculated the transition temperature using a simplified local random phase approximation procedure which accounts for the canting. For dilute magnetic semiconductors, such as GaMnAs, using ab initio couplings allows us to predict the existence of a canted phase and provides an explanation for the apparent contradictions observed in experimental measurements. Finally, we compared with previous studies that used Ruderman-Kittel-Kasuya-Yosida couplings and reported nonferromagnetic states when the superexchange is too strong. Even in this case the ferromagnetism should remain essentially stable in the form of a canted phase.