Manipulating the Voltage Dependence of Tunneling Spin Torques

Voltage-driven spin transfer torques in magnetic tunnel junctions provide an outstanding tool to design advanced spin-based devices for memory and reprogrammable logic applications. The non-linear voltage dependence of the torque has a direct impact on current-driven magnetization dynamics and on devices performances. After a brief overview of the progress made to date in the theoretical description of the spin torque in tunnel junctions, I present different ways to alter and control the bias dependence of both components of the spin torque. Engineering the junction (barrier and electrodes) structural asymmetries or controlling the spin accumulation profile in the free layer offer promising tools to design efficient spin devices.Comment: 10 pages, 4 figures, SPIE conference proceeding

Spin Transfer Torque in Antiferromagnetic Spin-Valves: From Clean to Disordered Regimes

Current-driven spin torques in metallic spin-valves composed of antiferromagnets are theoretically studied using the non-equilibrium Green's function method implemented on a tight-binding model. We focus our attention on G-type and L-type antiferromagnets in both clean and disordered regimes. In such structures, spin torques can either rotate the magnetic order parameter coherently (coherent torque) or compete with the internal antiferromagnetic exchange (exchange torque). We show that, depending on the symmetry of the spin-valve, the coherent and exchange torques can be either in the plane, {\alpha} n\times(q \times n) or out of the plane {\alpha} n \times q, where q and n are the directions of the order parameter of the polarizer and the free antiferromagnetic layers, respectively. Although disorder conserves the symmetry of the torques, it strongly reduces the torque magnitude, pointing out the need for momentum conservation to ensure strong spin torque in antiferromagnetic spin-valvesComment: 10 pages, 11 figure

Current-driven skyrmion Depinning in Magnetic Granular Films

We consider current-driven motion of magnetic skyrmions in granular magnetic films. The study uses micromagnetic modeling and phenomenological analysis based on the Thiele formalism. Remarkably, disorder enhances the effective skyrmion Hall effect that depends on the magnitude of the driving force (current density and non-adiabaticity parameter). The origin is sliding motion of the skyrmion along the grain boundaries, followed by pinning and depinning at the grain junctions. A side-jump can occur during this depinning process. In addition, the critical current that triggers the skyrmion motion depends on the relative size of the crystallites with respect to the skyrmion size. Finally, when the skyrmion trajectory is confined along an edge by the non-adiabatic Magnus force, the critical current density can be significantly reduced. Our results imply that narrow nanowires have higher skyrmion mobilities.Comment: 8 pages, 7 figure

On quantization of quadratic Poisson structures

Any classical r-matrix on the Lie algebra of linear operators on a real vector space V gives rise to a quadratic Poisson structure on V which admits a deformation quantization stemming from the construction of V. Drinfel'd. We exhibit in this article an example of quadratic Poisson structure which does not arise this way.Comment: Submitted to Comm. Math. Phys. Version 2 : error in introduction correcte

Voltage-driven v.s. Current-driven Spin Torque in Anisotropic Tunneling Junctions

Non-equilibrium spin transport in a magnetic tunnel junction comprising a single magnetic layer in the presence of interfacial spin-orbit interaction (SOI) is studied theoretically. The interfacial SOI generates a spin torque of the form {\bf T}=T_{||}{\bf M}x({\bf z}x{\bf M})+T_{\bot}{\bf z}x{\bf M}, even in the absence of an external spin polarizer. For thick and large tunnel barriers, the torque reduces to the perpendicular component, $T_{\bot}$, which can be electrically tuned by applying a voltage across the insulator. In the limit of thin and low tunnel barriers, the in-plane torque $T_{||}$ emerges, proportional to the tunneling current density. Experimental implications on magnetic devices are discussed.Comment: 5 pages, 5 figure