Hole Spin Polarization in AlAs / Ga 1 � x � y Mn x Al y As Structures

During the last years spin-polarized transport became a matter of major interest [1, 2], giving rise to a eld usually called magnetoelectronics, or spintronics. Much e ort has been made in studying and producing the so-called spin-valve, where a spin-polarized current is generated. A promising system in that area is the recently grown structure of GaAs/AlAs with inclusions of Ga1 xMnxAs layers [3, 4, 5, 6, 7]. Homogeneous samples of Ga1 xMn xAs alloys with x up to 7% have been produced, avoiding the formation of MnAs clusters by using low temperature (200 300 C) MBE techniques. In Ga1 xMnxAs, a new prototype of Diluted Magnetic Semiconductors (DMS), the Mn cations have the 3d shell partially lled with ve electrons, in such a way that they carry a magnetic moment of S = 5=2. In addition, the Mn ion binds a hole to satisfy charge neutrality. Besides its practical importance, this kind of DMS introduces an interesting problem from the physical point of view: Mn in the alloy is a strong p dopant, the free hole concentration reaching even p = 10 cm . At small Mn concentrations, the alloy is a paramagnetic insulator. As x increases it becomes ferromagnetic, going through a non-metal/metal transition for higher concentrations (x 0:03), and keeping its ferromagnetic phase. For x above 5%, the alloy becomes a ferromagnetic insulator. In the metallic phase, the ferromagnetic transition is observed in the range of 30 100K, depending on the value of x, among the highest transitions temperatures observed in DMS. The sp-d exchange interaction of Ruderman-Kittel-Kasuya-Yosida (RKKY) type has been recognized as the main origin of the observed ferromagnetism in the metallic phase of III-V based DMSs [6]. In the present work we consider a Ga1 xMnxAs layer in its metallic phase, grown inside a GaAs/AlAs quantum well structure. We obtain the spin-polarized electronic structure for holes, taking into account their interaction with the magnetic impurities. The Hamiltonian we consider is: