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Micromagnetics is a continuum theory describing magnetization patterns inside ferromagnetic media. The dynamics of a ferromagnetic material are governed by the Landau-Lifshitz equation. This equation is highly nonlinear and has a non-convex constraint. In this work, a finite element approximation of a current-induced magnetization dynamics model is proposed. The model consists of a modified Landau-Lifshitz-Gilbert (LLG) equation incorporating spin transfer torque. The scheme preserves a non-convex constraint, requires only a linear solver at each time step and is easily applicable to the limiting cases. As the time and space steps tend to zero, a proof of convergence of the numerical solution to a (weak) solution of the modified LLG equation is given. Numerical results are presented to show the effect of the injected current on magnetization switching. [ABSTRACT FROM AUTHOR]

Abstract: We theoretically study spin-polarized current through a single electron tunneling transistor (SETT), in which a quantum dot (QD) is coupled to non-magnetic source and drain electrodes via tunnel junctions, and gated by a ferromagnetic (FM) electrode. The I–V characteristics of the device are investigated for both spin and charge currents, based on the non-equilibrium Green''s function formalism. The FM electrode generates a magnetic field, which causes a Zeeman spin-splitting of the energy levels in the QD. By tuning the size of the Zeeman splitting and the source–drain bias, a fully spin-polarized current is generated. Additionally, by modulating the electrical gate bias, one can effect a complete switch of the polarization of the tunneling current from spin-up to spin-down current, or vice versa. [Copyright &y& Elsevier]

This paper deals with micromagnetic model of magnetization reversal in nano scale-point contact devices driven by nonuniform injection of a spin-polarized current. A computational study of the magnetization reversal in the nanosecond regime will be presented considering the influence of the current density distribution below the aperture region on the reversal time. For high current values, a strong dependence of the reversal time on the current distribution has been observed. Finally, results of micromagnetic simulations show that the reversal time versus current behaviour (at T = OK) is monotonic, very different from the switching processes observed in standard spin valves and magnetic tunnel junctions with uniform current injection. [ABSTRACT FROM AUTHOR]