Control of thermoelectric conversion of magnetic materials by direction of magnetization

Schematics of cooling induced by the anisotropic magneto-Thomson effect. Credit: Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.131.206701

The National Institute for Materials Science (NIMS) succeeded in directly observing the “anisotropic magneto-Thomson effect,” a phenomenon in which heat absorption/release is proportional to an applied temperature difference and charge current (ie, Thomson effect) changes. anisotropically dependent. in the direction of magnetization of magnetic materials.

This research is expected to lead to further progress in basic physics and materials science related to the fusion area of ​​thermoelectrics and spintronics, as well as to the development of new tools to control thermal energy using magnetism. The study was published in the journal Physical Review Letters.

The Thomson effect has long been known as one of the fundamental thermoelectric effects in metals and semiconductors, along with the Seebeck and Peltier effects, which drive the 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 explained how the Thomson effect is affected by magnetic fields and magnetism because the thermoelectric conversion of the Thomson effect in usually small and its measurement and quantitative. Estimation methods have not been fully established.

Under such conditions, NIMS reported in 2020 an experimental result in which the Thomson effect in nonmagnetic conductors was observed to change a magnetic field (ie, the magneto-Thomson effect).

This time, researchers succeeded in observing the anisotropic magneto-Thomson effect in magnetic materials through more accurate heat measurements. The anisotropic magneto-Thomson effect in magnetic materials is different from the usual magneto-Thomson effect in nonmagnetic materials, and this is the first direct observation of the unexplored phenomenon.

The NIMS research team used a thermal measurement technique called lock-in thermography to accurately measure the temperature distribution generated when a charge current is applied to the ferromagnetic alloy Ni.95Pt5 while applying a temperature difference, and verified how the Thomson effect changes depending on the direction of magnetization.

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

This research elucidates the fundamental properties of the anisotropic magneto-Thomson effect and establishes techniques for its quantitative measurement. In the future, researchers will continue to explore the physics, materials, and applications of the anisotropic magneto-Thomson effect to investigate new physics due to the interaction of heat, electricity, and magnetism, and to develop applications for thermal management technologies contribute to improving efficiency and conserving energy in electronic devices.

This project was carried out by 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).

More information:
Rajkumar Modak et al, Observation of the Anisotropic Magneto-Thomson Effect, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.131.206701

Provided by the National Institute for Materials Science

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