Dynamic relaxation of magnetic clusters in a ferromagnetic (Ga,Mn)As epilayer

TL;DR

This paper investigates the magnetic relaxation mechanisms in (Ga,Mn)As epilayers, proposing a cluster/matrix model and identifying the blocking temperature of magnetic clusters as key to understanding their ferromagnetic properties.

Contribution

It introduces a cluster/matrix model for (Ga,Mn)As ferromagnetism and demonstrates the significance of magnetic relaxation and interactions between clusters.

Findings

Magnetic relaxation similar to granular systems becomes significant above a certain temperature.

Magnetic interactions between clusters are significant below the higher-temperature peak.

The observed Curie temperature may actually be the blocking temperature of magnetic clusters.

Abstract

A new scenario of the mechanism of intriguing ferromagnetic properties in Mn-doped magnetic semiconductor (Ga,Mn)As is examined in detail. We find that magnetic features seen in zero-field cooled and field cooled magnetizations are not interpreted with a single domain model [Phys. Rev. Lett. 95, 217204 (2005)], and the magnetic relaxation, which is similar to that seen in magnetic particles and granular systems, is becoming significant at temperatures above the lower-temperature peak in the temperature dependence of ac susceptibility, supporting the cluster/matrix model reported in our previous work [Phys. Rev. Lett. 94, 147203 (2005)]. Cole-Cole analysis reveals that magnetic interactions between such (Ga,Mn)As clusters are significant at temperatures below the higher-temperature peak in the temperature dependent ac susceptibility. The magnetizations of these films disappear above the temperature showing the higher-temperature peak, which is generally referred to as the Curie temperature. However, we suggest that these combined results are evidence that the temperature is actually the blocking temperature of (Ga,Mn)As clusters with a relatively high hole concentration compared to the (Ga,Mn)As matrix.