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

Abstract

A scenario of the mechanism of intriguing ferromagnetic properties in Mn-doped magnetic semiconductor $(\mathrm{Ga},\mathrm{Mn})\mathrm{As}$ 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 $(\mathrm{Ga},\mathrm{Mn})\mathrm{As}$ 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 $(\mathrm{Ga},\mathrm{Mn})\mathrm{As}$ clusters with a relatively high hole concentration compared to the $(\mathrm{Ga},\mathrm{Mn})\mathrm{As}$ matrix.