Prospects of high temperature ferromagnetism in (Ga,Mn)As semiconductors

TL;DR

This study combines experimental and theoretical approaches to show that the Curie temperature in (Ga,Mn)As ferromagnetic semiconductors increases linearly with local moments, with room temperature ferromagnetism achievable at higher Mn concentrations.

Contribution

It provides a comprehensive analysis demonstrating that high-quality (Ga,Mn)As can reach room temperature ferromagnetism without fundamental doping limitations.

Findings

Curie temperature increases linearly with local Mn moments

Interstitial Mn acts as double-donors and causes compensation

Post-growth annealing removes compensating defects

Abstract

We report on a comprehensive combined experimental and theoretical study of Curie temperature trends in (Ga,Mn)As ferromagnetic semiconductors. Broad agreement between theoretical expectations and measured data allows us to conclude that T_c in high-quality metallic samples increases linearly with the number of uncompensated local moments on Mn_Ga acceptors, with no sign of saturation. Room temperature ferromagnetism is expected for a 10% concentration of these local moments. Our magnetotransport and magnetization data are consistnent with the picture in which Mn impurities incorporated during growth at interstitial Mn_I positions act as double-donors and compensate neighboring Mn_Ga local moments because of strong near-neighbor Mn_Ga-Mn_I antiferromagnetic coupling. These defects can be efficiently removed by post-growth annealing. Our analysis suggests that there is no fundamental obstacle to substitutional Mn_Ga doping in high-quality materials beyond our current maximum level of 6.2%, although this achievement will require further advances in growth condition control. Modest charge compensation does not limit the maximum Curie temperature possible in ferromagnetic semiconductors based on (Ga,Mn)As.