Spin-dependent properties of ferromagnetic/nonmagnetic GaAs heterostructures

We review recent studies on spin-dependent properties of structures made of ferromagnetic GaAs, (Ga,Mn)As, aimed to lay the ground for semiconductor spin-electronics (spintronics). Introduction of magnetic ion, Mn, in GaAs leads to hole-induced ferromagnetism, the origin of which is explained in terms of a mean-field theory. Due to exchange interaction between spins of carriers and localized magnetic electrons, spin-splitting of the semiconductor bands takes place when ferromagnetism sets in, and carriers become spin polarized. This spontaneous spin polarization leads to spin-dependent scattering and tunnel magnetoresistance in semiconducting structures. Electrical spin injection across a ferromagnetic/nonmagnetic semiconductor heterojunction and into an InGaAs quantum well is also demonstrated using the spin polarized carriers in ferromagnetic (Ga,Mn)As.