High Curie temperatures at low compensation in the ferromagnetic semiconductor (Ga,Mn)As

TL;DR

This study explores how the Curie temperature and electrical conductivity in (Ga,Mn)As ferromagnetic semiconductors increase with carrier density, challenging impurity band models and highlighting the importance of substitutional Mn acceptors.

Contribution

It provides experimental evidence linking higher Curie temperatures and conductivity to increased carrier density, emphasizing the role of substitutional Mn in (Ga,Mn)As.

Findings

Both TC and conductivity increase monotonically with p.

Maximum TC occurs when p is comparable to substitutional Mn concentration.

Results challenge impurity band models of ferromagnetism in (Ga,Mn)As.

Abstract

We investigate the relationship between the Curie temperature TC and the carrier density p in the ferromagnetic semiconductor (Ga,Mn)As. Carrier densities are extracted from analysis of the Hall resistance at low temperatures and high magnetic fields. Results are found to be consistent with ion channeling measurements when performed on the same samples. We find that both TC and the electrical conductivity increase monotonically with increasing p, and take their largest values when p is comparable to the concentration of substitutional Mn acceptors. This is inconsistent with models in which the Fermi level is located within a narrow isolated impurity band.