Single-material anomalous Nernst heat-flux sensor enabled by heat-assisted magnetization reversal

Abstract

Heat-flux sensors (HFSs) based on the transverse thermoelectric phenomenon of the anomalous Nernst effect have attracted increasing interest in recent years due to the advantages stemming from simple and planar sensor structures. However, the difference in Seebeck coefficients of the constituent materials makes the sensors also sensitive to an in-plane temperature gradient along the wire direction and can give rise to an undesirable offset in the sensor output. In this study, to mitigate this offset, improve structural efficiency, and simplify device fabrication, we propose a single-material anomalous Nernst HFS with antiparallel magnetization alignment in neighboring wires. Using heat-assisted magnetization reversal through electric-current-driven Joule heating, we were able to locally control the magnetization and realize such an antiparallel alignment in devices microfabricated from an L10-FePt thin film with an in-plane magnetic easy axis. Systematic measurements on a single FePt wire showed the conditions of electric current and magnetic field required for heat-assisted magnetization reversal; these conditions were then applied to a Π-shaped FePt element to selectively reverse one half of its magnetization and achieve antiparallel alignment. As a result, the Π-shaped element with antiparallel magnetization exhibits nearly twice the heat-flux sensitivity of a single wire. These results establish heat-assisted magnetization reversal as an effective way to locally control magnetization for constructing offset-free, single-material anomalous Nernst HFSs.