422 research outputs found
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, , 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 emerges,
proportional to the tunneling current density. Experimental implications on
magnetic devices are discussed.Comment: 5 pages, 5 figure
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