Ferromagnetism in manganese compound semiconductors not only opens prospects for tailoring magnetic and spin-related phenomena in semiconductors with a precision specific to III-V compounds but also addresses a question about the origin of the magnetic interactions that lead to a Curie temperature (T(C)) as high as 110 K for a manganese concentration of just 5%. Zener's model of ferromagnetism, originally proposed for transition metals in 1950, can explain T(C) of Ga(1-)(x)Mn(x)As and that of its II-VI counterpart Zn(1-)(x)Mn(x)Te and is used to predict materials with T(C) exceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.

(Accepted by PRB Rap. com.)We have calculated the spin-polarization effects of a current in a two dimensional electron gas which is contacted by two ferromagnetic metals. In the purely diffusive regime, the current may indeed be spin-polarized. However, for a typical device geometry the degree of spin-polarization of the current is limited to less than 0.1%, only. The change in device resistance for parallel and antiparallel magnetization of the contacts is up to quadratically smaller, and will thus be difficult to detect.Spin-polarized electron injection into semiconductors has been a field of growing interest during the last years [1][2][3][4]. The injection and detection of a spin-polarized current in a semiconducting material could combine magnetic storage of information with electronic readout in a single semiconductor device, yielding many obvious advantages. However, up to now experiments for spininjection from ferromagnetic metals into semiconductors have only shown effects of less than 1% [5,6], which sometimes are difficult to separate from stray-field-induced Hall-or magnetoresistance-effects [2]. In contrast, spininjection from magnetic semiconductors has already been demonstrated successfully [7,8] using an optical detection method.Typically, the experiments on spin-injection from a ferromagnetic contact are performed using a device with a simple injector-detector geometry, where a ferromagnetic metal contact is used to inject spin polarized carriers into a two dimensional electron gas (2DEG) [5]. A spin-polarization of the current is expected from the different conductivities resulting from the different densities of states) for spin-up and spin-down electrons in the ferromagnet. For the full device, this should result in a conductance which depends on the relative magnetization of the two contacts [1].A simple linear-response model for transport across a ferromagnetic/normal metal interface, which nonetheless incorporates the detailed behaviour of the electrochemical potentials for both spin directions was first introduced by van Son et al. [9]. Based on a more detailed (Boltzmann) approach, the model was developed further by Valet and Fert for all metal multilayers and GMR [10]. Furthermore, it was applied by Jedema et al. to superconductor-ferromagnet junctions [11]. For the interface between a ferromagnetic and a normal metal, van Son et al. obtain a splitting of the electrochemical potentials for spinup and spindown electrons in the region of the interface. The model was applied only to a single contact and its boundary resistance [9]. We now apply a similar model to a system in which the material properties differ considerably.Our theory is based on the assumption that spinscattering occurs on a much slower timescale than other electron scattering events [12]. Under this assumption, two electrochemical potentials µ ↑ and µ ↓ , which need not be equal, can be defined for both spin directions at any point in the device [9]. If the current flow is one dimensional in the x-direction, the electroc...

Recent works aiming at understanding magnetotransport phenomena in ferromagnetic III-V and II-VI semiconductors are described. Theory of the anomalous Hall effect in p-type magnetic semiconductors is discussed, and the relative role of side-jump and skew-scattering mechanisms assessed for (Ga,Mn)As and (Zn,Mn)Te. It is emphasized that magnetotransport studies of ferromagnetic semiconductors in high magnetic fields make it possible to separate the contributions of the ordinary and anomalous Hall effects, to evaluate the role of the spins in carrier scattering and localization as well as to determine the participation ratio of the ferromagnetic phase near the metal-insulator transition. A sizable negative magnetoresistance in the regime of strong magnetic fields is assigned to the weak localization effect.