Measuring entropy generated by spin-transfer

TL;DR

This paper introduces an experimental method to measure entropy generated by spin-transfer in ferromagnetic nanostructures, revealing that spin-transfer causes incoherent excitations rather than uniform magnetization rotation.

Contribution

The study presents a novel protocol for quantifying spin-transfer-induced entropy in ferromagnetic nanowires using thermal susceptibility measurements.

Findings

Spin-transfer generates incoherent excitations.

Entropy can be measured via thermal susceptibility.

Incoherent excitations dominate over magnetization rotation.

Abstract

An experimental protocol is presented that allows the entropy generated by spin-transfer to be measured. The effect of a strong spin-polarized current injected on a ferromagnetic nanostructure is investigated with focusing on the quasi-static equilibrium states of a ferromagnetic single domain. The samples are single contacted Ni nanowires obtained by electrodeposition in a nanoporous template. The thermal susceptibility of the magnetoresistance is measured as a function of the magnetic field for different values of the current injected through the wire. This quantity is related to the thermal magnetic susceptibility of the ferromagnetic wire through the anisotropic magnetoresistance. The ferromagnetic entropy generated by the current injection is deduced thanks to a thermodynamic Maxwell relation. This study shows that the effect of the spin-transfer in our samples results in the generation of incoherent excitations instead of rotation of the magnetization.