Negative Anomalous Nernst Effect Signals in Mixed-Phase (110)-Oriented FeRh Films Grown on Al₂O₃ Substrates

By measuring the anomalous Nernst effect (ANE), which is a result of a spontaneous drop in the transverse voltage driven by the temperature gradient in a magnetic material, over a temperature range of 100–350 K, we observed the ANE thermopower in (110)-oriented FeRh films on Al₂O₃substrates, with similar magnetic transport behaviors observed for in-plane magnetization (IM) and out-of-plane magnetization (PM) configurations. The temperature-dependent magnetization–magnetic field strength (M-H) curves revealed that the ANE voltage was proportional to the magnetization of the material, but additional features magnetic textures not shown in the M-H curves remained intractable. In particular, a sign reversal occurred for the ANE thermopower signal near zero field in the mixed-magnetic-phase films at low temperatures, which was attributed to the diamagnetic properties of the Al₂O₃ substrate. Finite element method simulations associated with the Heisenberg spin model and Landau–Lifshitz–Gilbert equation strongly supported the abnormal heat transport behavior from the Al₂O₃ substrate during the experimentally observed magnetic phase transition for the IM and PM configurations. Our results demonstrate that FeRh films on an Al₂O₃ substrate exhibit unusual behavior compared to other ferromagnetic materials, indicating their potential for use in novel applications associated with practical spintronics device design, neuromorphic computing, and magnetic memory.