Structural and magnetic phase stability of group IV/MnAs superlattices for spintronics applications

Results of first-principles electronic structure calculations and experiments on molecular beam epitaxy grown samples of Group IV/MnAs superlattices where Group IV=Si and Ge are reported. The structural and magnetic phase stabilities were determined by total energy and atomic force calculations using the full-potential linearized augmented plane-wave (FLAPW) method within the generalized gradient approximation. The zincblende MnAs layers in these superlattices showed interesting behavior, such as different magnetic phase transitions and half-metallicity where the competition between the exchange interaction of Mn atoms through direct d-d and indirect p-d channels played an important role. For example, for the Si/MnAs case, the antiferromagnetic (AFM) ground state makes a transition to a ferromagnetic (FM) phase upon a 2% tetragonal distortion. A comparison of the electronic structures of the Si/MnAs and Ge/MnAs superlattices exhibits the dependence of the magnetism and the magnetic phase stability on the interatomic distance as well as on the host anion. Experimental results on the Si/MnAs superlattice revealed that AFM ordering is found to be stable over the FM phase while the Ge/MnAs superlattice showed a dominant FM phase at zero temperature.