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arXiv · 2310.02070

Controlled Quasi-Latitudinal Solutions for ultra-fast Spin-Torque Precessional Magnetization Switching

Alessandro Fortunati·Massimiliano d'Aquino·Claudio Serpico
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Abstract

The aim of the paper is to present a novel class of time-dependent controls to realize ultra-fast magnetization switching in nanomagnets driven by spin-torques produced by spin-polarized electric currents. Magnetization dynamics in such systems is governed by the Landau-Lifshitz-Slonczewski equation which describes the precessional motion of (dimensionless) magnetization vector on the unit-sphere. The relevant case of nanoparticles with uniaxial anisotropy having in-plane easy and intermediate axes and out-of-plane hard axis is considered. By exploiting the characteristic smallness of damping and spin-torque intensity, the aforementioned controls are constructed via suitable perturbative tools in a way to realise approximate \emph{latitudinal solutions} (i.e. motions on a sphere in which the out-of-plane magnetization component stays constant) with the effect to fast ``switch'' the system from one stationary state to another. The possibility to keep a (``small'') bounded value of the out-of-plane coordinate throughout this process of ``transfer'', turns out to be advantageous in the applications as it sensibly reduces the post-switching relaxation oscillations that may cause the failure of switching in real samples. Further relevant quantitative results on the behaviour of the solutions during the pre- and post-switching stages (termed ``expulsion'' and ``attraction'', respectively), are given as a byproduct. A selection of validating numerical experiments is presented alongside the corresponding theoretical results.

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Alessandro Fortunati, Massimiliano d'Aquino, Claudio Serpico. 2023-10-03. Controlled Quasi-Latitudinal Solutions for ultra-fast Spin-Torque Precessional Magnetization Switching. https://doi.org/10.1142/s0218127424500561

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