Conventional computer electronics creates a dichotomy between how information is processed and how it is stored. Silicon chips process information by controlling the flow of charge through a network of logic gates. This information is then stored, most commonly, by encoding it in the orientation of magnetic domains of a computer hard disk. The key obstacle to a more intimate integration of magnetic materials into devices and circuit processing information is a lack of efficient means to control their magnetization. This is usually achieved with an external magnetic field or by the injection of spin-polarized currents [1,2,3]. The latter can be significantly enhanced in materials whose ferromagnetic properties are mediated by charge carriers [4]. Among these materials, conductors lacking spatial inversion symmetry couple charge currents to spin by intrinsic spin-orbit (SO) interactions, inducing nonequilibrium spin polarization [5,6,7,8,9,10,11] tunable by local electric fields. Here we show that magnetization of a ferromagnet can be reversibly manipulated by the SO-induced polarization of carrier spins generated by unpolarized currents. Specifically, we demonstrate domain rotation and hysteretic switching of magnetization between two orthogonal easy axes in a model ferromagnetic semiconductor.In crystalline materials with inversion asymmetry, intrinsic spin-orbit interactions (SO) couple the electron spin with its momentumhk. The coupling is given by the Hamiltonian H so =h 2σ · Ω(k), whereh is the Planck's constant andσ is the electron spin operator (for holesσ should be replaced by the total angular momentum J). Electron states with different sign of the spin projection on Ω(k) are split in energy, analogous to the Zeeman splitting in an external magnetic field. In zinc-blende crystals such as GaAs there is a cubic Dresselhaus term[12] Ω D ∝ k 3 , while strain introduces a term Ω ε = C∆ε(k x , −k y , 0) that is linear in k, where ∆ε is the difference between strain in theẑ andx,ŷ directions [13]. In wurzite crystals or in multilayered materials with structural inversion asymmetry there also exists the Rashba term[14] Ω R which has a different symmetry with respect to the direction of k,, whereẑ is along the axis of reduced symmetry. In the presence of an electric field the electrons acquire an average momentumh∆k(E), which leads to the generation of an electric current j =ρ −1 E in the conductor, whereρ is the resistivity tensor. This current defines the preferential axis for spin precession Ω(j) . As a result, a nonequilibrium current-induced spin polarization J E Ω(j) is generated, whose magnitude J E depends on the strength of various mechanisms of momentum scattering and spin relaxation [5,15]. This spin polarization has been measured in non-magnetic semiconductors using optical [7,8,9,11,16] and electron spin resonance [17] techniques. It is convenient to parameterize J E in terms of an effective magnetic field H so . Different contributions to H so have different current dependencies (∝ j or j 3 ), as we...
