Nonequilibrium phase transitions in ferromagnetic semiconductors (EuO1–δ)

Abstract

The features of metal-semiconductor kinetic phase transformation in ferromagnetic semiconductors are studied. It is shown that heat release caused by current results in a positive feedback between the current density and the sample temperature, magnetization, and thermal-spin fluctuation amplitude. The Joule heating of the sample leads to disappearance of magnetization and, as a result, to restoration of the forbidden band between the conduction and valence bands. However, the energy gap width continues to change due to an increase in the fluctuations of internal exchange fields splitting the electron states. Within the framework of the developed model, an S-shaped volt-ampere characteristic is obtained for a EuO 1-δ , ferromagnetic semiconductor. The lower branch of the characteristic corresponds to a ferromagnetic metal state (a “cold” phase) and the upper one is due to a semiconductor paramagnetic state (a “hot” phase).