Controlling thermoelectric conversion in magnetic materials by direction of magnetization

The National Institute of Materials Science (NIMS) managed to directly observe the “anisotropic magneto-Thomson effect”, a phenomenon in which the absorption/release of heat proportional to an applied temperature difference and charging current (i.e. the Thomson effect) changes anisotropically depending on the ambient temperature. on the direction of magnetization in magnetic materials.

This research is expected to lead to the development of fundamental physics and materials science related to the field of fusion of thermoelectrics and spintronics, as well as the development of new functionalities to control thermal energy with magnetism. The study is published in the journal Physical Examination Letters.

The Thomson effect has long been known as one of the fundamental thermoelectric effects in metals and semiconductors, alongside the Seebeck and Peltier effects, which are the driving principles of thermoelectric conversion technologies.

Although the influence of magnetism on the Seebeck and Peltier effects has been studied for many years, it has not been clarified how the Thomson effect is affected by magnetic fields and magnetism, because the thermoelectric conversion of the Thomson effect is generally small and its extent and quantity are measured. estimation methods are not fully established.

Under such circumstances, NIMS in 2020 reported an experimental result in which the Thomson effect in non-magnetic conductors was observed to change with a magnetic field (i.e. the magneto-Thomson effect) .

This time, the researchers managed to observe the anisotropic magneto-Thomson effect in magnetic materials thanks to more precise thermal measurements. The anisotropic magneto-Thomson effect in magnetic materials differs from the conventional magneto-Thomson effect in non-magnetic materials, and this is the first direct observation of this unexplored phenomenon.

The NIMS research team used a thermal measurement technique called gated thermography to precisely measure the temperature distribution generated when a charging current is applied to a ferromagnetic Ni alloy.₉₅Pt₅ while applying a temperature difference, and checked how the Thomson effect evolves as a function of the direction of the magnetization.

As a result, it was found that the amount of heat absorption (or heat release) generated in the Ni₉₅Pt₅ The alloy is larger when the temperature gradient and charging current are parallel to the magnetization than when they are perpendicular to the magnetization. This result is consistent with the expected behavior of measurements of Seebeck and Peltier effects in magnetic materials.

This research has clarified the fundamental properties of the anisotropic magneto-Thomson effect and established techniques for its quantitative measurement. In the future, researchers will continue to explore the physics, materials and functionalities of the anisotropic magneto-Thomson effect to study new physics caused by the interaction of heat, electricity and magnetism, and to develop applications for thermal management technologies that will help improve the efficiency and energy conservation of electronic devices.

This project was carried out by Rajkumar Modak (Special Researcher, CMSM Magnetic and Spintronic Materials Research Center), NIMS), Takamasa Hirai (Researcher, CMSM, NIMS), Seiji Mitani (Director, CMSM, NIMS) and Ken-ichi Uchida. (Distinguished Group Leader, GSMR, NIMS).