Electronic Structure and Magnetism of New Ferromagnetic Semiconductors

" The injection of spins into nonmagnetic semiconductors has recently attracted great interest due to the potential to create new classes of spin-dependent electronic devices. For ferromagnetic (FM) metals (i.e., Fe) as spin sources, however, the spin orientation of the carriers tends to be quickly lost at a ferromagnet-semiconductor interface via spin-flip scattering due to the dissimilar crystal structure and chemical bonding, modified surface magnetism (i.e. for Fe, FM changes to AFM at the surface), and the energy difference between the charge carriers in the ferromagnet and the semiconductor. A recent strategy is to achieve spin injected semiconductors, so called, diluted ferromagnetic semiconductor (DFS), prepared by substituting magnetic ions such as V, Cr, Mn, Fe, Co, and Ni into non-magnetic semiconductors. Ferromagnetism was reported in various semiconductors such as group II-VI, III-V, IV, and II-IV-V2, etc. However, the low solubility of magnetic ions in non-magnetic semiconductors limits its usuage as a large spin polarizer. Recently four new chalcopyrite compounds (MnGeP2, MnGeAs2, MnSnP2, and MnSnAs2) have been synthesized and the transition temperatures were measured to be 300, 333, 305, and 328 K. Two of them (MnGeP2 and MnGeAs2) are semiconductors, while the others (MnSnP2, and MnSnAs2) are metallic. Spin polarized current has been observed in MnGeP2 and MnGeAs2 magnetic tunnel junctions. In this talk, we will present the calculational results on the electronic structures and magnetisms of the new chalcopyrite magnetic compounds, using the Full Potential Linearized Augmented Plane Wave(FLAPW) method, based on local spin density approximation(LSDA). "