Spin polarization control via magnetic barriers and spin-orbit effects

Abstract

We investigate the spin-dependent transport properties of two-dimensional electron gas (2DEG) systems formed in diluted magnetic semiconductors and in the presence of Rashba spin-orbit interaction in the framework of the scattering matrix approach. We focus on nanostructures consisting of realistic magnetic barriers produced by the deposition of ferromagnetic strips on heterostructures. We calculate spin-dependente conductance of such barrier systems and show that the magnetization pattern of the strips, the tunable spin-orbit coupling, and the enhanced Zeeman splitting have a strong effect on the conductance of the structure. We describe how these effects can be employed in the efficient control of spin polarization via the application of moderate fields. PACS numbers: 71.70.Ej, 73.23.Ad, 72.25.-b, 72.10.-d Spin-orbit coupling in semiconductors intrinsically connects the spin of an electron to its momentum, 1 providing a pathway for electrically initializing and manipulating electron spins for applications in spintronics 2,3 and spin-based quantum information processing. 4 This coupling can be regulated with quantum confinement in semiconductor heterostructures through band structure engineering, as well as by the application of external electric fields, as in the celebrated spin field-effect transistor proposed by Datta and Das. 5 Using diluted magnetic semiconductors (DMS) in such systems provides an additional degree of control of the transport properties. In particular, when an external magnetic field is applied, the magnetic dopant spins align, giving rise to a strong exchange field that acts on the electron spin. This sd exchange interaction between the electron spin in the conduction band and the localized magnetic ions induces a giant Zeeman splitting. In this communication we investigate the spindependent transport properties of two-dimensional electron gas (2DEG) systems formed in diluted magnetic semiconductors and take into account the electric-field– dependent Rashba spin-orbit (SOI) interaction. We focus our attention on nanostructures consisting of realistic magnetic barriers produced by the deposition of ferromagnetic strips near the heterostructures, 6 providing a relatively strong inhomogeneous magnetic field on the 2DEG. We show how the conductance of the 2DEG depends strongly on the magnetization pattern of the strips, as well as on geometry and externally applied electric fields. We demonstrate that significant spin polarization (exceeding 50%) can be obtained at low temperatures for ferromagnetic strips of typical dimensions and magnetization.