Abnormal Magnetic Phase Transition in Mixed‐Phase (110)‐Oriented FeRh Films on Al2O3 Substrates via the Anomalous Nernst Effect

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 20; no. 43; pp. e2403315 - n/a
• Main Authors: Choi, Jae Won, Park, Chanho, Kim, Gil‐Sung, Cho, Jung‐Min, Park, No‐Won, Kim, Yun‐Ho, Jung, Min Young, Chang, Seo Hyoung, Akhanda, Md Sabbir, Shivaram, Bellave, Bennett, Steven P., Zebarjadi, Mona, Lee, Sang‐Kwon
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.10.2024
• Subjects: Aluminum oxide; anomalous Nernst effect; Configurations; Curie temperature; Diamagnetism; Ferromagnetic materials; Ferromagnetic phases; Field strength; Finite element method; Heisenberg spin model; Landau–Lifshitz–Gilbert equation; Low temperature; magnetic phase transition; Magnetic properties; Magnetization; Nernst-Ettingshausen effect; Phase transitions; Rhodium; Spintronics; Temperature; Temperature dependence; Thermoelectricity; Transport phenomena
• ISSN: 1613-6810; 1613-6829; 1613-6829
• DOI: 10.1002/smll.202403315

Iron rhodium (FeRh) undergoes a first‐order anti‐ferromagnetic to ferromagnetic phase transition above its Curie temperature. By measuring the anomalous Nernst effect (ANE) in (110)‐oriented FeRh films on Al2O3 substrates, the ANE thermopower over a temperature range of 100–350 K is observed, 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 is 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 is 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. The 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. Here, the anomalous Nernst effect in the 25‐nm‐thick (110)‐oriented FeRh thin films is observed, 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. To elucidate the causes of this phenomenon further, various experimental and theoretical analyses are successfully performed.