Current induced Spin Torque in a nanomagnet

TL;DR

This paper derives a comprehensive model for current-induced spin torque in nanomagnets, revealing complex hysteresis and multiple stable magnetic states due to Coulomb blockade effects.

Contribution

It introduces a unified equation for magnetization dynamics considering transport and magnetic properties, highlighting Coulomb blockade's role in spin torque behavior.

Findings

Multiple stable magnetic states can coexist under certain conditions.

Coulomb blockade influences the structure of spin torque.

Hysteresis effects are significant in nanomagnet dynamics.

Abstract

In a nanomagnet (whose total spin S< 1000), very small polarized currents can lead to magnetic reversal. Treating on the same footing the transport and magnetic properties of a nanomagnet connected to magnetic leads via tunneling barriers, we derive a closed equation for the time evolution of the magnetization. The interplay between Coulomb blockade phenomena and magnetism gives some additional structure to the current induced spin torque. In addition to the possibility of stabilizing uniform spin waves, we find that the system is highly hysteretic: up to three different magnetic states can be simultaneously stable in one region of the parameter (magnetic field and bias voltage) space.