Quantum Dynamics of a Nanomagnet driven by Spin-Polarized Current

TL;DR

This paper develops a quantum theory describing how spin-polarized currents influence nanomagnet magnetization, revealing both average behavior and quantum fluctuations, including noise effects.

Contribution

It introduces a quantum framework for nanomagnet dynamics driven by spin-polarized currents, capturing both average motion and quantum noise effects.

Findings

Quantum trajectory aligns with semi-classical spin transfer torque in large spin limit.

Reveals quantum magnetization noise and current noise contributions.

Provides a probabilistic description of magnetization recoil states.

Abstract

A quantum theory of magnetization dynamics of a nanomagnet as a sequence of scatterings of each electron spin with the macrospin state of the magnetization results in each encounter a probability distribution of the magnetization recoil state associated with each outgoing state of the electron. The quantum trajectory of the magnetization contains the average motion tending in the large spin limit to the semi-classical results of spin transfer torque and the fluctuations giving rise to a quantum magnetization noise and an additional noise traceable to the current noise.