Andre Petukhov

Self-compensation in manganese-doped ferromagnetic semiconductors

We present a theory of interstitial Mn in Mn-doped ferromagnetic semiconductors. Using density-functional theory, we show that under the nonequilibrium conditions of growth, interstitial Mn is easily formed near the surface by a simple low-energy adsorption pathway. In GaAs, isolated interstitial Mn is an electron donor, each compensating two substitutional Mn acceptors. Within an impurity-band model, partial compensation promotes ferromagnetic order below the metal-insulator transition, with the highest Curie temperature occurring for 0.5 holes per substitutional Mn.

Thermodynamics of Carrier-Mediated Magnetism in Semiconductors

We propose a model of carrier-mediated ferromagnetism in semiconductors that accounts for the temperature dependence of the carriers. The model permits analysis of the thermodynamic stability of competing magnetic states, opening the door to the construction of magnetic phase diagrams. As an example, we analyze the stability of a possible reentrant ferromagnetic semiconductor, in which increasing temperature leads to an increased carrier density such that the enhanced exchange coupling between magnetic impurities results in the onset of ferromagnetism as temperature is raised.