Current-induced asymmetric magnetoresistance due to energy transfer via quantum spin-flip process

TL;DR

This paper presents experimental evidence that energy transfer via quantum spin-flip processes causes asymmetric magnetoresistance in ferromagnet/heavy metal bilayers, independent of spin-transfer torque effects, and suggests a new way to generate THz magnons using dc currents.

Contribution

It demonstrates that energy transfer through quantum spin-flip processes significantly influences magnetoresistance, revealing a novel mechanism beyond spin-transfer torque in magnetic nanostructures.

Findings

Magnetoresistance depends on current direction at low currents.

Energy transfer via quantum spin-flip explains observed MR asymmetry.

Potential for dc-current-induced THz magnon generation.

Abstract

Current-induced magnetization excitation is a core phenomenon for next-generation magnetic nanodevices, and has been attributed to the spin-transfer torque (STT) that originates from the transfer of the spin angular momentum between a conduction electron and a local magnetic moment through the exchange coupling. However, the same coupling can transfer not only spin but also energy, though the latter transfer mechanism has been largely ignored. Here we report on experimental evidence concerning the energy transfer in ferromagnet/heavy metal bilayers. The magnetoresistance (MR) is found to depend significantly on the current direction down to low in-plane currents, for which STT cannot play any significant role. Instead we find that the observed MR is consistent with the energy transfer mechanism through the quantum spin-flip process, which predicts short wavelength, current-direction-dependent magnon excitations in the THz frequency range. Our results unveil another aspect of current-induced magnetic excitation, and open a channel for the dc-current-induced generation of THz magnons.