Electrical rectification effect in single domain magnetic microstrips: a micromagnetics-based analysis

TL;DR

This paper uses micromagnetic analysis to investigate electrical rectification in magnetic microstrips, finding that Oersted fields, rather than spin transfer torque, likely explain the observed voltage signals.

Contribution

The study provides a quantitative micromagnetic analysis showing that Oersted fields, not spin transfer torque, account for the rectification effect in magnetic microstrips.

Findings

Spin transfer torque signals are too weak to explain experiments.

A small average Oersted field aligns with experimental data.

Contacts likely generate the Oersted field responsible for rectification.

Abstract

Upon passing an a.c. electrical current along magnetic micro- or nanostrips, the measurement of a d.c. voltage that depends sensitively on current frequency and applied field has been recently reported by A. Yamaguchi and coworkers. It was attributed to the excitation of spin waves by the spin transfer torque, leading to a time-varying anisotropic magnetoresistance and, by mixing of a.c. current and resistance, to a d.c. voltage. We have performed a quantitative analysis by micromagnetics, including the spin transfer torque terms considered usually, of this situation. The signals found from the spin transfer torque effect are several orders of magnitude below the experimental values, even if a static inhomogeneity of magnetization (the so-called ripple) is taken into account. On the other hand, the presence of a small non-zero average Oersted field is shown to be consistent with the full set of experimental results, both qualitatively and quantitatively. We examine, quantitatively, several sources for this average field and point to the contacts to the sample as a likely origin.