Efficient room-temperature magnetization direction detection by means of the enhanced anomalous Nernst effect in a Weyl ferromagnet

Abstract

Spintronic phenomena exhibiting a longitudinal resistance change under magnetization reversal are a quite novel feature in nanoscience, which has been intensively studied in hopes of realizing all-electrical magnetization direction detection devices, where no reference ferromagnetic layer is required. However, cryogenic temperatures and/or high magnetic fields have been required to achieve noticeable effects. Here, the high heat-to-charge conversion efficiency of the Heusler alloy Weyl semimetal Co₂MnGa is exploited in single layer nanoscaled wires at room temperature to produce at least two orders of magnitude enhancement of the resistance change ratio, when compared with conventional ferromagnets. Such resistance change under magnetization reversal is consistently explained through temperature distribution simulations and direct thermoelectric measurements of the large anomalous Nernst effect (ANE) in this topologically nontrivial material. Although many reports consider ANE signals as perturbations or undesired artifacts, we demonstrate that they are dominant in this system and can be seized for nonvolatile memory readout, as shown in a prototype device. These results open up new horizons of using enhanced thermoelectric voltages in novel materials for magnetization direction detection in any system where significant temperature gradients exist.