---
author:
- 'D. M. Edwards'
- 'F. Federici'
title: 'Current-driven switching of magnetisation- theory and experiment'
---

Introduction {#intro}
============

Recently there has been a lot of interest in magnetic nanopillars of 10-100 nm in diameter. The pillar is a metallic layered structure with two ferromagnetic layers, usually of cobalt, separated by a non-magnetic spacer layer, normally of copper. Non-magnetic leads are attached to the magnetic layers so that an electric current may be passed through the structure. In the simplest case the pillar may exist in two states, with the magnetisation of the two magnetic layers parallel or anti-parallel. The state of a pillar can be read by measuring its resistance, this being smaller in the parallel state than in the anti-parallel one. This dependence of the resistance on magnetic configuration is the giant magnetoresistance (GMR) effect [@1]. A dense array of these nanopillars could form a magnetic memory for a computer. Normally one of the magnetic layers in a pillar is relatively thick and its magnetisation direction is fixed. In order to write into the memory the magnetisation direction of the second thinner layer must be switched. This might be achieved by a local magnetic field of 