The National Institute for Materials Science (NIMS) has achieved a significant milestone in the field of thermoelectric conversion by directly observing the anisotropic magneto-Thomson effect. This phenomenon refers to the changes in heat absorption/release, proportional to an applied temperature difference and charge current, that depend on the magnetization direction in magnetic materials.
The implications of this research extend to the advancement of basic physics and materials science in the fusion area of thermoelectrics and spintronics. Furthermore, it opens doors to the development of new functionalities for controlling thermal energy using magnetism. The study documenting these findings has been published in the journal Physical Review Letters.
The Thomson effect, alongside the Seebeck and Peltier effects, is a well-known fundamental thermoelectric effect in metals and semiconductors. These effects are the driving principles behind thermoelectric conversion technologies.
While the influence of magnetism on the Seebeck and Peltier effects has been extensively studied, the impact of magnetic fields and magnetism on the Thomson effect has remained unclear. This is primarily due to the relatively small thermoelectric conversion of the Thomson effect and the lack of established methods for its measurement and quantitative estimation.
Addressing this gap, NIMS reported in 2020 an experimental result showcasing the change in the Thomson effect in nonmagnetic conductors under the influence of a magnetic field, known as the magneto-Thomson effect.
Building upon this previous research, the NIMS research team has now successfully observed the anisotropic magneto-Thomson effect in magnetic materials by employing more precise thermal measurements. Unlike the conventional magneto-Thomson effect observed in nonmagnetic materials, the anisotropic magneto-Thomson effect in magnetic materials represents an unexplored phenomenon, making this direct observation groundbreaking.
To achieve these observations, the NIMS research team utilized a thermal measurement technique known as lock-in thermography. This technique enabled the accurate measurement of the temperature distribution generated when a charge current was applied to a ferromagnetic alloy, specifically Ni95Pt5, while maintaining a temperature difference. The team then verified how the Thomson effect varied depending on the magnetization direction.
The results revealed that the amount of heat absorption (or release) in the Ni95Pt5 alloy was greater when the temperature gradient and charge current were parallel to the magnetization compared to when they were perpendicular to it. This finding aligns with the anticipated behavior observed in measurements of the Seebeck and Peltier effects in magnetic materials.
This research has not only shed light on the fundamental properties of the anisotropic magneto-Thomson effect but has also established techniques for its quantitative measurement. Moving forward, the NIMS research team aims to delve deeper into the physics, materials, and functionalities associated with this effect. Their goal is to investigate the new physics that emerge from the interaction of heat, electricity, and magnetism. Additionally, they seek to develop applications for thermal management technologies that can enhance efficiency and contribute to energy conservation in electronic devices.
The research project was conducted by a team consisting of Rajkumar Modak (Special Researcher, Research Center for Magnetic and Spintronic Materials CMSM, NIMS), Takamasa Hirai (Researcher, CMSM, NIMS), Seiji Mitani (Director, CMSM, NIMS), and Ken-ichi Uchida (Distinguished Group Leader, CMSM, NIMS).
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