Spin-Transfer Torque Magnetization Reversal in Uniaxial Nanomagnets with Thermal Noise

TL;DR

This paper develops an analytical approach to understand magnetization switching times in uniaxial nanomagnets influenced by spin-torque and thermal noise, validated by GPU simulations, revealing effects of geometrical tilts and slow asymptotic behavior.

Contribution

The paper introduces an explicit analytical solution for thermally assisted switching times in uniaxial nanomagnets with spin-torque, incorporating geometrical tilt effects and validated by GPU-based stochastic LLG simulations.

Findings

Switching times can be described similarly in tilted and collinear cases.

Thermal noise significantly influences the crossover from deterministic to thermally assisted reversal.

Asymptotic behavior is reached slowly, affecting switching time predictions.

Abstract

We consider the general Landau-Lifshitz-Gilbert (LLG) dynamical theory underlying the magnetization switching rates of a thin film uniaxial magnet subject to spin-torque effects and thermal fluctuations (thermal noise). After discussing the various dynamical regimes governing the switching phenomena, we present analytical results for the mean switching time behavior. Our approach, based on explicitly solving the first passage time problem, allows for a straightforward analysis of the thermally assisted, low spin-torque, switching asymptotics of thin film magnets. To verify our theory, we have developed an efficient GPU-based micromagnetic code to simulate the stochastic LLG dynamics out to millisecond timescales. We explore the effects of geometrical tilts between the spin-current and uniaxial anisotropy axes on the thermally assisted dynamics. We find that even in the absence of axial symmetry, the switching times can be functionally described in a form virtually identical to the collinear case. We further verify that asymptotic behavior is reached fairly slowly, thus quantifying the role of thermal noise in the crossover regime linking deterministic to thermally assisted magnetization reversal.