Magnetic Material with Macroscale, Three-Dimensional Formation of Nano-Interfaces That Turn Heat into Electricity

Thermoelectric conversion, which utilizes the vast amounts of waste heat and unused heat around us as electric energy, is one of the key technologies for improving energy-use efficiency and achieving carbon neutrality. The spin Seebeck effect is a physical phenomenon discovered in Japan in 2008, where applying a temperature gradient to a magnetic material enables thermoelectric conversion via spin currents. However, as conventional spin Seebeck devices used a layered structure consisting of a magnetic material and a thin metal film, they had limitations in increasing the output power by increasing device thickness or adding further layers.

In this study, the research team coated the surface of the yttrium iron garnet (YIG) powders, a magnetic insulator, with platinum (Pt), and sintered them at low temperature under high pressure, to develop a bulk composite in which YIG/Pt nanoscale interfaces are distributed throughout the material in three dimensions. Unlike in conventional thin-film layered devices, this composite can achieve thermoelectric conversion by the spin Seebeck effect using the interfaces distributed throughout the bulk (Figure). The team demonstrated that the spin Seebeck effect is generated in the fabricated YIG-Pt bulk composite, and showed that the utilization of the metal channels distributed within the material facilitates scaling up in the thickness direction. This research has demonstrated the concept of the trans-scale spin Seebeck effect, which extends a nanoscale interfacial phenomenon to macroscale energy conversion.

This work demonstrated that, by forming nanoscale interfaces throughout a material in three dimensions, a spin-based thermoelectric phenomenon previously limited to thin-film interfaces can be extended to a bulk material. In the future, the thermoelectric conversion performance is expected to improve further through optimization of the design and control of the three-dimensional interface structure and the materials. We demonstrated the conversion of thermal energy in an insulator into electrical energy in a macroscopic material, which is difficult to achieve using conventional thermoelectric technologies. This finding opens a path toward new thermal management devices.

• This project was conducted by a team of researchers including Sang Jun Park (Postdoctoral Research Fellow, Research Center for Magnetic and Spintronic Materials [CMSM], NIMS), Ken-ichi Uchida (Distinguished Group Leader, CMSM, NIMS [Professor, Department of Advanced Materials Science (AMS), Graduate School of Frontier Science (GSFS), The University of Tokyo]), and Keisuke Hirata (Assistant Professor, AMS, GSFS, The University of Tokyo [at the start of the research, Assistant Professor, Toyota Technological Institute]). The work was supported by JST Strategic Basic Research Programs ERATO "UCHIDA Magnetic Thermal Management Materials Project" (Research Director: Ken-ichi Uchida; Grant No.:JPMJER2201).
• This research result was published in Nature Communications on July 21, 2026.