Spin-Dependent Phenomena in (Ga,Mn)As Heterostructures

Abstract

A model for spin-dependent tunneling in semiconductor heterostruc- tures, which combines a multi-orbital empirical tight-binding approach with a Landauer{Buttiker formalism, is presented. Using this approach we ex- plain several phenomena observed in modulated structures of (Ga,Mn)As, i.e., large values of the electron current spin polarization in magnetic Esaki{ Zener diode and the high tunneling magnetoresistance ratio. Next, the rel- evance of this theory to assess the tunneling anisotropic magnetoresistance efiect is studied. The results of applying the tight-binding model to describe the recently observed interlayer exchange coupling in (Ga,Mn)As-based su- perlattices are also shown. Gallium arsenide doped with manganese is a ∞ag member of the group of semiconductors which at low temperatures exhibit ferromagnetism. These so-called diluted ferromagnetic semiconductors are mainly III{V compounds with part of the cations substituted by magnetic ions. Since the discovery of such mate- rials at the 90-ties of previous century, the ferromagnetic p-type (Ga,Mn)As is by far the most studied and best understood | for (Ga,Mn)As also the highest tem- perature of the transition to the ferromagnetic phase (173 K) has been achieved (1). (Ga,Mn)As owes his unique position to the ability to form high quality junctions with nonmagnetic GaAs or AlAs, due to similar crystal structure of these com- pounds. Intensive studies of such multilayers with modulated magnetization have proven that most of the phenomena essential for realizing functional spintronic devices can be observed also in these all-semiconductor heterostructures. These include flrst of all an e-cient electrical injection of spin-polarized carriers | spin injection from p-(Ga,Mn)As into nonmagnetic semiconductor has been achieved