Structural stability and half-metallicity of the zinc-blende phase of Al1-xCrxAs: Density-functional study

An accurate full-potential linear augmented plane waves method has been used to investigate the structural stability, half-metallic ferromagnetism of the zinc-blende phase of the ferromagnetic semiconductor alloy Al1-xCrxAs. The relative stability of the zinc-blende phase with respect to the NiAs one and the ferromagnetism to the antiferromagnetism are confirmed by comparing total energy of various structures. Full optimization for all these structures is performed, including the cell volume, c/a for tetrahedral cells and internal parameters. Our calculation shows that when the Cr composition is less than 30%, the zinc-blende phase is more stable, whereas the NiAs one is more stable for more Cr composition. Therefore, bulk Al1-xCrxAs with zinc-blende structure can be obtained when x is smaller than 0.3, whereas only epitaxial films can exist for larger x. For all these compounds with x ranging from 0.125 to 1.0, robust half-metallic ferromagnetism is found in the zinc-blende phase. In addition, the effects of the spin-orbital interaction are considered and the total magnetic moments including both the spin and orbital contributions are presented. The spin-orbital interaction will destroy the perfect half-metallic ferromagnetism by reflecting some majority-spin states into the minority-spin gap, however, the decrease of the spin-polarization is only about 0.2% for all substitutional cases. At last, we give the exchange parameters and consecutively the Curie temperature within the mean-field approximation. Our systematical calculation for Al1-xCrxAs is useful to elucidate the half-metallic ferromagnetism in Al1-xCrxAs and to explore high-performance spintronic devices based on Al1-xCrxAs in future information technologies.