Compositional dependence of ferromagnetism in (Al,Ga,Mn)As magnetic semiconductors

We report on a detailed study of the magnetic, electrical, and structural properties of the quaternary ferromagnetic semiconductor (Al,Ga,Mn)As. We investigate films with Al concentration y varying from 0.05 to 1, with a fixed total Mn density. The ferromagnetic transition temperature Tc decreases with increasing Al concentration, with no ferromagnetism observed at y=0.5 and y=0.75 for as-grown and annealed films, respectively. Detailed measurements identify three mechanisms giving rise to a suppression of Tc on alloying with Al: an increased tendency for Mn to occupy compensating interstitial sites, an increased stability of interstitials against annealing, and an increased localization of carriers. These studies serve as a test of the validity of theories of ferromagnetism in III-V semiconductors across different chemical compositions and represent a starting point for the development of new GaAs/(Al,Ga)As ferromagnetic heterostructures. © 2008 The American Physical Society.