We introduce a new class of spintronics devices in which a spin-valve like effect results from strong spin-orbit coupling in a single ferromagnetic layer rather than from injection and detection of a spin-polarized current by two coupled ferromagnets. The effect is observed in a normalmetal/insulator/ferromagnetic-semiconductor tunneling device. This behavior is caused by the interplay of the anisotropic density of states in (Ga,Mn)As with respect to the magnetization direction, and the two-step magnetization reversal process in this material.PACS numbers: 75.50. Pp, 85.75.Mm Devices relying on spin manipulation are hoped to provide low-dissipative alternatives for microelectronics. Furthermore, spintronics is expected to lead to full integration of information processing and storage functionalities opening attractive prospects for the realization of instant on-and-off computers. A primary goal of current spintronics research is to realize a device with metal spin-valve like behavior [1] in an all semiconductor-based structure enhancing integration of spintronics with existing microelectronics technologies. An oft proposed scheme for such a device consists of a tunnel barrier between two ferromagnetic semiconductors. As such, (Ga,Mn)As/(Al,Ga)As/(Ga,Mn)As structures have previously been studied [2,3] with some promising results. However, realizing the full potential of these systems will require a complete understanding of the physics of tunneling into (Ga,Mn)As, which we have found to be rather different than previously thought.In this spirit, we investigate transport in a structure consisting of a single ferromagnetic (Ga,Mn)As layer fitted with a tunnel barrier and a non-magnetic metal contact. We report some of the rich experimental properties of such a tunneling structure and provide an interpretation of the measured spin-valve like effect as a tunneling anisotropic magnetoresistance (TAMR) due to a two-step magnetization reversal and a magnetization dependent density of states (DOS) in the (Ga,Mn)As layer.The magnetic layer in our sample is a 70 nm thick epitaxial (Ga,Mn)As film grown by low temperature (270• C) molecular beam epitaxy onto a GaAs (001) substrate [4]. High-resolution x-ray diffraction showed that the sample had high crystalline quality comparable to that of the substrate. From the measured lattice constant and the calibration curves of Ref.[5], the Mn concentration in the ferromagnetic layer is roughly 6%. Etch capacitance-voltage control measurements yielded a hole density estimate of ∼ 10 21 cm −3 and the Curie temperature of 70 K was determined from SQUID measurements.After growth, the sample surface was Ar sputtered to remove any potential oxides, and a 1.4 nm Al layer was deposited at a rate of 0.

It is demonstrated by SQUID magnetization measurements that (Ga,Mn)As films can exhibit rich characteristics of magnetic anisotropy depending not only to the epitaxial strain but being strongly influenced by the hole and Mn concentration, and temperature. This behavior reflects the spin anisotropy of the valence subbands and corroborates predictions of the mean field Zener model of the carrier mediated ferromagnetism in III-V diluted magnetic semiconductors with Mn. At the same time the existence of in-plane uniaxial anisotropy with [110] the easy axis is evidenced. This is related to the top/bottom symmetry breaking, resulting in the lowering of point symmetry of (Ga,Mn)As to the C2v symmetry group. The latter mechanism coexists with the hole-induced cubic anisotropy, but takes over close to TC.PACS numbers: 75.50. Pp, 75.30.Gw, 73.61.Ey, The discovery of carrier-mediated ferromagnetism at temperatures in excess of 100 K in (III,Mn)V dilute magnetic semiconductors (DMS) grown by molecular beam epitaxy (MBE) has made it possible to combine complementary properties of semiconductor quantum structures and ferromagnetic systems in single devices, paving the way for the development of functional semiconductor spintronics.1 Therefore, the understanding of magnetic anisotropy in these systems and the demonstration of methods for its control is timely and important. It has been known, since the pioneering works of Munekata et al.2 and Ohno et al., 3 that ferromagnetic (In,Mn)As and (Ga,Mn)As films are characterized by a substantial magnetic anisotropy. Remarkably, due to magnetic dilution, the ordinary shape anisotropy plays here only a marginal role and, accordingly, explains neither direction nor large magnitude of the observed anisotropy field H un .It has been found by anomalous Hall effect studies, 3 that the direction of the easy axis is mainly controlled by epitaxial strain in these systems. Generally, for layers under tensile biaxial strain [like (Ga,Mn)As on a (In,Ga)As buffer] perpendicular-to-plane magnetic easy axis has been observed (perpendicular magnetic anisotropy, PMA). In contrast, layers under compressive biaxial strain [as canonical (Ga,Mn)As on a GaAs substrate] have been found to develop in-plane magnetic easy axis (in-plane magnetic anisotropy, IMA). At first glance, this sensitivity to strain appears surprising, as the Mn ions are in the orbital singlet state 6 A 1 . For such a state, the strain-induced single ion anisotropy is expected to be rather small and, indeed, electron paramagnetic resonance (EPR) studies of Mn in GaAs yielded relevant spin Hamiltonian parameters by two orders of magnitude too small to explain the observed values of H un . 4In the system in question, however, the ferromagnetic spin-spin exchange interaction is mediated by the band holes, whose Kohn-Luttinger amplitudes are primarily built up of anion p orbitals in tetrahedrally coordinated semiconductors. Furthermore, in semiconductors, in contrast to metals, the Fermi energy is usually smaller than the atomic spin-orbit...

We report the discovery of a very large tunneling anisotropic magnetoresistance in an epitaxially grown (Ga,Mn)As/GaAs/(Ga,Mn)As structure. The key novel spintronics features of this effect are as follows: (i) both normal and inverted spin-valve-like signals; (ii) a large nonhysteretic magnetoresistance for magnetic fields perpendicular to the interfaces; (iii) magnetization orientations for extremal resistance are, in general, not aligned with the magnetic easy and hard axis; (iv) enormous amplification of the effect at low bias and temperatures.

Giant magnetic linear dichroism (MLD) is observed in the ferromagnetic semiconductor Ga 0:98 Mn 0:02 As. The contribution to this effect induced by the spontaneous magnetization can be clearly identified by azimuthal dependencies. The spectral dependence of the effect in the range from 1.4 to 2.4 eV shows that the MLD induced by the spontaneous magnetization is strongly enhanced for excitations from the electronic states that are responsible for the ferromagnetism in this material. This spectral sensitivity and the size of the effect makes MLD a powerful tool for the study of III; MnV alloys and similar novel ferromagnetic semiconductors.

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