Magnetic multilayers in Ga1-xMn xAs/GaAs struc

Abstract

Mn in GaAs substitutes Ga as a p dopant and introduces a localized magnetic moment of 5/2. Ga1–xMnxAs (for x » 0.04) has been proved to be an extremely interesting material, for its intrincated transport and magnetic properties. In the first part of this work a structure is considered in which a series of Ga1–xMnxAs layers is grown inside a GaAs quantum well. The electron-electron interaction through a Hartree potential, together with the magnetic interaction with the DMS layers (assumed in the ferromagnetic phase) produces an e effctive potential corresponding to a sequence of small barriers which depend (height and width) on the hole spin orientation. For a large number of such layers it is shown that the model structure approaches a magnetic superlattice. A self-consistent calculation is performed for the electronic structure, resulting into spin-polarized energy levels. The polarized miniband Bloch transport properties are calculated for different structural arrangements. In the second part we calculate the transversal spin polarized current induced by an applied voltage through an AlAs/Ga1–xMnxAs/AlAs double barrier heterostructure (DBH). The magnetic layer is assumed in its metallic and ferromagnetic phase. As a consequence of the magnetic interaction a strong polarization of the hole subbands inside the quantum well. In that case the resonant tunneling occurs at different voltages for different spin orientation (parallel or anti-parallel to the average magnetization of Ga1–xMnxAs) throughout. Based on a many-body field quantization formalism that makes use of the tight binding method we obtain, in an essentially exact way, an analytic expression for the spin polarized tunneling current and the escape rate from the right barrier of the DBH. The characteristic spin polarized I(V) curves, as well as the relaxation times, are obtained for different hole concentrations and magnetic layer widths, providing important informations for the possibility of building spin valves made those materials.