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

TLDR

The study investigates Curie temperature trends in (Ga,Mn)As ferromagnetic semiconductors through combined experimental and theoretical analysis. The authors attribute magnetic behavior to interstitial Mn acting as double donors that compensate substitutional Mn moments via antiferromagnetic coupling, and show that post‑growth annealing can efficiently eliminate these defects. They find that Tc rises linearly with uncompensated Mn_Ga moments without saturation, predicting room‑temperature ferromagnetism at 10% local moments, and conclude that higher substitutional Mn doping is feasible and charge compensation does not limit the maximum Tc.

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 ${\mathrm{Mn}}_{\mathrm{Ga}}$ 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 consistent with the picture in which Mn impurities incorporated during growth at interstitial ${\mathrm{Mn}}_{\mathrm{I}}$ positions act as double-donors and compensate neighboring ${\mathrm{Mn}}_{\mathrm{Ga}}$ local moments because of strong near-neighbor ${\mathrm{Mn}}_{\mathrm{Ga}}{\mathrm{Mn}}_{\mathrm{I}}$ antiferromagnetic coupling. These defects can be efficiently removed by post-growth annealing. Our analysis suggests that there is no fundamental obstacle to substitutional ${\mathrm{Mn}}_{\mathrm{Ga}}$ doping in high-quality materials beyond our current maximum level of 6.8%, 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.