Ab initio transport theory for digital ferromagnetic heterostructures.

We present a theoretical density functional study of the electronic, magnetic, and transport properties of digital ferromagnetic heterostructures, obtained by delta doping GaAs with Mn. In the absence of intrinsic donors these systems have a half metallic density of states, with an exchange interaction much stronger than that of a random alloy with the same Mn concentration. Our ab initio ballistic transport calculations show that the carriers at the Fermi energy are strongly confined within a few monolayers around the MnAs plane. This strong confinement is responsible for the large exchange coupling and the two-dimensional half metallic behavior.