Spin Torque for Dummies

Published

January 6, 2007

Author(s)

Thomas J. Silva

Abstract

I will present a stripped down presentation on the fundamental mechanisms that give rise to spin torque effects. This presentation will assume the audience has little or no background in this fascinating and rapidly expanding field. We will start with an introduction to the nature of spin dynamics in ferromagnetic metals. In particular, We will review the nature of damped gyromagnetic motion of the magnetization in an effective field and the Landau-Lifshitz formulation for magnetization dynamics. Next, We will cover the basic properties of spin transport in ferromagnetic heterostructures, including the spin-split bands in itinerant ferromagnets and how that leads to spin accumulation in nonmagnetic metal spacer layers. By invoking conservation of angular momentum, we obtain the spin transfer torque, which can be succinctly described as an additional term in the gyromagnetic equation of motion: The so-called Slonczewski term. Finally, I will explain why we have only recently observed this effect since the phenomenon is most often manifested as spontaneous dynamics when current densities exceed 10⁷ A/cm². Thus, spin torque is a nanotechnological consequence of driven electron transport in ferromagnetic structures. I will present experimental data from our labs at NIST-Boulder on the performance of spin torque nano-oscillators and a quick summary of device physics and properties.

Citation

IEEE Magnetics Society

Pub Weblink

http://www.ieeemagnetics.org/

Pub Type

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Keywords

Ferromagnetics, gyromagnetic, nano-oscillators, spin torque

Citation

Silva, T. (2007), Spin Torque for Dummies, IEEE Magnetics Society, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=32601, http://www.ieeemagnetics.org/ (Accessed October 31, 2024)