Current-Induced Effective Magnetic Fields in Co/Cu/Co Nanopillars

TL;DR

This paper introduces a measurement technique to distinguish spin-transfer effects from charge-current magnetic fields in Co/Cu/Co nanopillars, revealing a current-dependent effective magnetic field that influences magnetization switching.

Contribution

The study develops a method to measure spin-current induced effective magnetic fields, providing new insights into spin-transfer phenomena in nanopillar structures.

Findings

Current-dependent hysteresis loop shifts attributed to spin-transfer

Effective magnetic field magnitude estimated at ~1.5 x 10^{-7} Oe cm^2/A

Spin-transfer induced field is about one-fifth of the torque magnitude

Abstract

We present a method to measure the effective field contribution to spin-transfer-induced interactions between the magnetic layers in a trilayer nanostructure, which enables spin-current effects to be distinguished from the usual charge-current-induced magnetic fields. This technique is demonstrated on submicron Co/Cu/Co nanopillars. The hysteresis loop of one of the magnetic layers in the trilayer is measured as a function of current while the direction of magnetization of the other layer is kept fixed, first in one direction and then in the opposite direction. These measurements show a current-dependent shift of the hysteresis loop which, based on the symmetry of the magnetic response, we associate with spin-transfer. The observed loop-shift with applied current at room temperature is reduced in measurements at 4.2 K. We interprete these results both in terms of a spin-current dependent effective activation barrier for magnetization reversal and a spin-current dependent effective magnetic field. From data at 4.2 K we estimate the magnitude of the spin-transfer induced effective field to be $\sim 1.5 \times 10^{-7} $ Oe cm$^2$/A, about a factor of 5 less than the spin-transfer torque.