Spin-Transfer Torques Generated by the Anomalous Hall Effect and Anisotropic Magnetoresistance

Tomohiro Taniguchi, J. Grollier, and M. D. Stiles
Phys. Rev. Applied 3, 044001 – Published 6 April 2015

Abstract

Spin-orbit coupling in ferromagnets gives rise to the anomalous Hall effect and the anisotropic magnetoresistance, both of which can be used to create spin-transfer torques in a similar manner as the spin Hall effect. In this paper, we show how these effects can be used to reliably switch perpendicularly magnetized layers and to move domain walls. A drift-diffusion treatment of the anomalous Hall effect and the anisotropic magnetoresistance describes the spin currents that flow in directions perpendicular to the electric field. In systems with two ferromagnetic layers separated by a spacer layer, an in-plane electric field causes spin currents to be injected from one layer into the other, creating spin-transfer torques. Unlike the related spin Hall effect in nonmagnetic materials, the anomalous Hall effect and the anisotropic magnetoresistance allow control of the orientation of the injected spins, and hence torques, by changing the direction of the magnetization in the injecting layer. The torques on one layer show a rich angular dependence as a function of the orientation of the magnetization in the other layer. The control of the torques afforded by changing the orientation of the magnetization in a fixed layer makes it possible to reliably switch a perpendicularly magnetized free layer. Our calculated critical current densities for a representative CoFe/Cu/FePt structure show that the switching can be efficient for appropriate material choices. Similarly, control of the magnetization direction can drive domain-wall motion, as shown for NiFe/Cu/NiFe structures.

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  • Received 18 November 2014

DOI:https://doi.org/10.1103/PhysRevApplied.3.044001

© 2015 American Physical Society

Authors & Affiliations

Tomohiro Taniguchi

  • National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Tsukuba, Ibaraki 305-8568, Japan and Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6202, USA

J. Grollier

  • Unité Mixte de Physique CNRS/Thales and Université Paris Sud 11, 1 Avenue Fresnel, 91767 Palaiseau, France

M. D. Stiles

  • Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6202, USA

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Vol. 3, Iss. 4 — April 2015

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