Energy dissipation and switching delay in spin-transfer torque switching of nanomagnets with low-saturation magnetization in the presence of thermal fluctuations

TL;DR

This paper investigates how increasing spin-polarized current during switching can maintain consistent delay and variance in nanomagnets with low saturation magnetization, reducing energy dissipation despite thermal noise effects.

Contribution

It introduces a method to compensate for increased switching delay and variance in low-$M_s$ nanomagnets by pumping excess spin-polarized current, improving energy efficiency.

Findings

Pumping excess spin current stabilizes switching delay and variance.

Reducing $M_s$ lowers energy dissipation significantly.

Thermal noise effects are modeled with stochastic LLG equations.

Abstract

A common ploy to reduce the switching current and energy dissipation in spin-transfer-torque driven magnetization switching of shape-anisotropic single-domain nanomagnets is to employ magnets with low saturation magnetization $M_s$ and high shape-anisotropy. The high shape-anisotropy compensates for low $M_s$ to keep the static switching error rate constant. However, this ploy increases the switching delay, its variance in the presence of thermal noise, and the dynamic switching error rate. Using the stochastic Landau-Lifshitz-Gilbert equation with a random torque emulating thermal noise, we show that pumping some excess spin-polarized current into the nanomagnet during switching will keep the mean switching delay and its variance constant as we reduce $M_s$, while still reducing the energy dissipation significantly.