We study the transport properties of a spin filter consisting of a double-barrier resonant tunneling device in which the well is made of a semimagnetic material. Even if the device could be made of several materials, we discuss here the case of a Ga1-xMn xAs/Ga1-yAl yAs system because it can be integrated into the well known AlAs/GaAs technology. We solve the Hamiltonian H = H K+H P+H E+H M+Hh-i+Hh-h. Its terms represent the kinetic energy, the double-barrier profile, the applied bias, the magnetic interaction, the hole-impurity attraction and the hole-hole repulsion, respectively. A very simple one-dimensional Green function is introduced to solve self-consistently the Poisson equation for the profile due to the charge distribution. A real space renormalization formalism is used to calculate exactly the currents. In a previous work we have shown that the Rashba effect is weak. Therefore the results show very well defined spin-polarized currents. Our results confirm that this system is a good device for spintronics.

A double barrier resonant tunneling device in which the well is made of a semi-magnetic material can work as an efficient spin filter. Today it is possible to make semiconductors that are ferromagnetic at room temperature. Therefore the device studied here has a great potential to be used as a polarizer, an analyzer and other spintronic applications. We discuss here the case of a Ga1-xMn xAs/Ga1-yAl yAs system because it can be integrated into the well known AlGaAs/GaAs technology. Our tight-binding Hamiltonian includes the kinetic energy, the double-barrier profile, the electric field, the magnetic term, the hole-impurity and the hole-hole interactions. The profile and the charge distribution are calculated self-consistently. In previous works we studied this system by solving the Hamiltonian in the reciprocal space, in order to simplify the treatment of the Poisson equation for the charge distribution. Here we introduce a simple one dimensional Green function that permits to solve all terms in the real space. Besides, a real space renormalization formalism is used to calculate exactly the electronic currents for each spin polarization. The results confirm that the proposed system is a good device for spintronics.

Mn in GaAs substitutes Ga as a p dopant and introduces a localized magnetic moment of 5<img src="http:/img/fbpe/bjp/v32n2a/a54img01.gif" align="absMiddle">/2. Ga1–xMn xAs (for x <FONT FACE=Symbol>»</font> 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–xMn xAs 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–xMn xAs/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–xMn xAs) 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.

A self-consistent calculation of the electronic properties of GaAlAs:Mn magnetic semiconductor quantum well structures is performed including the Hartree term and the sp-d exchange interaction with the Mn magnetic moments. The spin polarization density is obtained for several structure configurations.

Using the balance of forces in the linear regime, it is shown that the ratio between the induced voltage in an open circuit Coulomb drag experiment, and the induced current in closed circuit, equals the internal resistence of the circuit in which the induction occurs.