Enhancement of ferromagnetic coupling in Mn/GaAs digital ferromagnetic heterostructure by free-hole injection

We have studied the effect of the free-hole injection on the ferromagnetic coupling in the Mn/GaAs digital ferromagnetic heterostructure (DFH) using ab initio electronic-structure methods. The DFH is modeled by a supercell periodically consisting of a delta-doped layer of MnAs and 15 layers of GaAs. The injection of free holes is simulated by assigning a range of missing electrons in unit cell. The delta-doped layer of Mn atoms in GaAs introduces three spin-polarized hole bands which are the consequence of hybridization between the d states of the Mn atoms and the p states of the nearest neighboring As atoms. These spin-polarized holes are confined to the vicinity of the MnAs layer. After the injection of free holes, the Fermi energy is lowered, consequently the number of spin-polarized holes in the layer of MnAs increases monotonously. Our results show the enhancement of the ferromagnetic coupling by the free-hole injection, which is in agreement with the experimental observation. (C) 2006 American Institute of Physics.