Fundamental Curie temperature limit in ferromagnetic GaMnAs

TL;DR

This study demonstrates that the maximum Curie temperature in GaMnAs is limited by Fermi-level-induced hole saturation, with experimental evidence linking Mn interstitials and hole concentration to the Fermi level position.

Contribution

It reveals the fundamental limit of Curie temperature in GaMnAs is due to Fermi-level effects on Mn interstitial formation, providing insights into ferromagnetic material design.

Findings

Curie temperature limit around 110 K in GaMnAs.

Fermi level controls Mn interstitial formation and hole saturation.

Increasing Be does not raise free hole concentration, affecting T_C.

Abstract

We provide experimental evidence that the upper limit of ~110 K commonly observed for the Curie temperature T_C of Ga(1-x)Mn(x)As is caused by the Fermi-level-induced hole saturation. Ion channeling, electrical and magnetization measurements on a series of Ga(1-x-y)Mn(x)Be(y)As layers show a dramatic increase of the concentration of Mn interstitials accompanied by a reduction of T_C with increasing Be concentration, while the free hole concentration remains relatively constant at ~5x10^20 cm^-3. These results indicate that the concentrations of free holes and ferromagnetically active Mn spins are governed by the position of the Fermi level, which controls the formation energy of compensating interstitial Mn donors.