Anomalous Nernst effect in Fe-Si alloy films

Abstract

The anomalous Nernst effect (ANE), one of the long-studied thermomagnetic effects, has been regarded as a promising next-generation energy harvesting technology for large-area and flexible devices. However, since the ANE power is too short for practical use, it is necessary to enhance ANE and many ferromagnetic materials have been widely investigated [1].We experimentally investigated the anomalous Nernst effect (ANE) in an Fe3Si film whose ANE was predicted to be large, based on the topological band structure [2]. We also measured the Seebeck and anomalous Hall effects to separate the ANE term from the Hall effect of the carrier flow induced by the Seebeck effect. The sample structure and measurement system are shown in Fig. 1. In addition to Fe3Si, Fe2Si, FeSi, and FeSi2 50nm films were fabricated on SiO2 substrate by co-sputtering and annealed in vacuum at 1123K for 1 hour.Figure 2 shows the ANE coefficient as a function of Si composition in Fe-Si compounds. The ANE coefficients were estimated as 1.0 and 0.5 µVK-1 for the Fe3Si and Fe2Si samples, respectively. These values are much larger than the ANE coefficient of film Fe, whereas Fe3Si and Fe2Si both have a smaller saturation magnetization than Fe. In general, the Nernst coefficient can be decomposed into two terms: Syx= ρxxαyx - tanθAHESxx. Here, the first term S1 exhibits the intrinsic ANE term that converts heat flow into a transverse voltage, and the second term S2 reflects the voltage originating from the Hall effect of the carrier flow induced by the Seebeck effect during the anomalous Nernst effect. From Fig. 2, it was found that the first term S1 was dominant in the ANE improvement of Fe3Si, suggesting that the ANE of Fe3Si is enhanced because of its band structure, as expected from the theoretical calculation.Fig.1 Schematics of the sample structure and ANE measurement configuration.Fig.2 Negative value of the ANE coefficient Sxy, the first term S1 , and the second term S2 as a function of Si composition in Fe-Si compounds.  Fig.1 Schematics of the sample structure and ANE measurement configuration.  Fig.2 Negative value of the ANE coefficient Sxy, the first term S1 , and the second term S2 as a function of Si composition in Fe-Si compounds.