GaMnAs

GaMnAs, or gallium manganese arsenide, is a dilute magnetic semiconductor formed by substituting manganese into gallium arsenide (GaAs). It is typically prepared by low-temperature molecular beam epitaxy, which stabilizes Mn on substitutional gallium sites and yields a material that combines semiconducting behavior with ferromagnetic order.

Mn in GaAs provides localized magnetic moments and acts as an acceptor, introducing holes that mediate exchange between Mn moments. A portion of Mn atoms occupy interstitial sites and act as double donors, compensating holes and suppressing magnetism; annealing lowers the concentration of interstitial Mn, increases hole density, and raises the Curie temperature.

Ferromagnetism in GaMnAs is widely interpreted as carrier-mediated. The magnetic coupling between Mn moments is thought to be mediated by holes in the valence band (or a Mn-induced impurity band) and is described by p-d exchange or Zener-type models. The resulting Curie temperature in high-quality films is well below room temperature, with early studies reporting around 110 K and optimized samples reaching roughly 150–180 K.

Electronic and transport properties are strongly influenced by compensation and disorder. GaMnAs is usually semiconducting or insulating at low Mn concentrations, with a pronounced anomalous Hall effect and magneto-optical responses that enable studies of spin polarization and ferromagnetism.

GaMnAs serves as a primary model system for spintronics research and the study of carrier-mediated ferromagnetism in semiconductors. While its Curie temperatures remain well below ambient, the material has informed development of dilute magnetic semiconductors and related spintronic concepts.