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

TL;DR

This paper models the magnetic interactions in Mn-rich Mn(Ga)As nanoclusters within GaAs, revealing that size variations and modified RKKY interactions can lead to spin-glass behavior and potentially higher Curie temperatures.

Contribution

It introduces a modified RKKY model considering carrier contributions inside nanoclusters, explaining spin-glass behavior and suggesting ways to enhance ferromagnetism.

Findings

Modified RKKY oscillation can change sign due to carrier concentration differences.

Size distribution of nanoclusters influences spin frustration and magnetic behavior.

Tuning nanocluster sizes can restore ferromagnetism with higher Curie temperatures.

Abstract

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.