Spin-glass-like behavior caused by Mn-rich Mn(Ga)As nanoclusters in GaAs

We simulate the indirect exchange interaction between Mn-rich Mn(Ga)As nanoclusters in GaAs by analytical means. In contrast to the conventional Ruderman-Kittel-Kasuya-Yosida (RKKY) formula which considers the mediation by the carriers in the medium, we also include the contribution from those inside the clusters. Since the carrier concentration is higher in the clusters, this modification allows the RKKY oscillation to change sign. Consequently, while the previous approach only favors ferromagnetism for this system, an antiferromagnetic coupling is in fact possible. Since the Mn-rich Mn(Ga)As nanoclusters are naturally formed and bound to have different sizes, their spin orientation is likely to be frustrated due to mixed preferences from different neighbors. We argue that this is likely the source of the spin-glass-like behavior which plagues this system. By tuning the size and narrowing its distribution, normal ferromagnetism can be restored with an Curie temperature higher than previously thought.