Magnetic states of transition metal impurities in silicon carbide

Electronic properties of 3C silicon carbide with substitutional transition metal impurities are calculated using an ab initio full-potential linearized augmented plane wave technique. It is shown that transition metal atoms in an SiC host may exist in both magnetic and nonmagnetic states. For different impurity species, the transition from the nonmagnetic to the magnetic state and the corresponding change of the atomic magnetic moments may take place either gradually as the volume of the unit cell changes or when the energy gap between the two states is overcome. The magnetic and nonmagnetic solutions are characterized by significantly different unit cell geometries, which are analysed in detail. Magnetic ordering is studied for a number of transition metal impurities in SiC and mean-field estimates of the Curie temperature are given. Calculated densities of states are used to analyse the nature of the exchange interaction between the impurities. Some properties of transition metal impurities are compared for 3C and 4H silicon carbide substitution.