Giant and Robust Anomalous Nernst Effect in a Polycrystalline Topological Ferromagnet at Room Temperature

• Published in: Advanced functional materials Vol. 32; no. 49
• Main Authors: Feng, Zili, Minami, Susumu, Akamatsu, Shuhei, Sakai, Akito, Chen, Taishi, Nishio‐Hamane, Daisuke, Nakatsuji, Satoru
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.12.2022
• Subjects: Electronic structure; Ferromagnetism; ferromagnets; Hall effect; Magnets; Materials science; Nernst effect; Nernst-Ettingshausen effect; nodal lines; polycrystalline alloys; Polycrystals; Robustness; Room temperature; Single crystals; thermoelectrics; Thermopiles; Topology; Transport properties
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202206519

Recent discoveries of the topological magnets have opened a new path for developing a much simpler thermoelectric conversion module using the anomalous Nernst effect (ANE). To accelerate such innovation, it is essential to design materials suitable for industrial processes, and thus a high‐ANE polycrystalline material has been highly desired. Recently, the giant room‐temperature ANE has been reported in single crystals of the topological ferromagnet Fe3Ga. Owning to its cubic structure, the anomalous Hall effect and ANE are isotropic. These properties potentially allow to employ a polycrystalline form of the material to design an ANE‐based thermopile. Here, a giant and robust room‐temperature ANE in the polycrystalline FexGa4−x (2.96 < x < 3.15) is reported, which can be enhanced up to 5.4 µV K−1; this value hits the highest room‐temperature record for polycrystalline magnets. Comparison of the experimental results with the theoretical study of the Fe‐doping effect on the transport properties of FexGa4−x reveals that the Fermi energy tuning near the topological nodal‐web structure is the key to enhancing the ANE. Moreover, the large value of more than 5.1 µV K−1 is observed for an extended region of composition, confirming the robust characteristics of the topological electronic structure. The largest room‐temperature anomalous Nernst effect among polycrystalline magnets, 5.4 µV K–1, is found in Fe3.09Ga0.91. It is robust against Fe doping as the nodal web band shifts toward the Fermi level meanwhile the nodal web remains intact. The excellent performance, low cost, and nontoxicity make this topological magnet a most promising candidate for energy‐harvesting devices and heat‐current sensors.