Demonstrating a Novel Method to Modulate Heat Flow Through the Collective Motion of Spins

Thermal conductivity is a fundamental parameter characterizing heat conduction in a solid. The primary heat carriers are known to be electrons and phonons, quasiparticles corresponding to lattice vibrations. In current thermal engineering, efforts are underway to modulate thermal conductivity and interfacial thermal resistance by elucidating and controlling the transport properties of heat carriers. In particular, heat conduction modulation focusing on the transport and scattering of phonons has been actively studied over the past decades as "phonon engineering." While heat carriers other than electrons and phonons also contribute to heat conduction, they have largely been disregarded as their contribution is extremely small in most materials, only being observed under extreme environments, such as at a very low temperature, if at all.

In this study, the research team demonstrated that heat conduction can be modulated by utilizing and controlling the transport of "magnons"—quasiparticles corresponding to the collective motion of spins in a magnetic material—in a simple structure formed by stacking a thin film of a ferromagnetic metal, such as a cobalt-iron alloy (CoFe) or a nickel-iron alloy (NiFe), on an insulator. The team revealed that, when non-equilibrium magnon currents generated in the ferromagnetic metal propagate to the insulator (Figure (a)), the thermal conductivity of the ferromagnetic metal thin film increases, compared to when they do not (Figure (b)), even at room temperature, with the interfacial thermal resistance at the metal/insulator junction reduced to as low as a fraction of the original level (Figure). The research result shows that thermal transport engineering through control of magnon transport (magnon engineering) is applicable even to metals in which electrons are dominant heat carriers, upsetting the conventional wisdom that magnon contribution to heat conduction in metals is extremely small at room temperature.

Based on this research result, the team aims to further elucidate the physical origin of this mechanism, and to create new heat modulation technologies applying "magnon engineering", such as a thermal switch in which the magnon transport is controlled through an external field.

• This research was conducted by a team of researchers including Takamasa Hirai (Senior Researcher, Spin Caloritronics Group (SCG), Research Center for Magnetic and Spintronic Materials (CMSM), NIMS), Toshiaki Morita (Trainee, SCG, CMSM, NIMS; a doctoral student, SANKEN, the University of Osaka), Ken-ichi Uchida (Distinguished Group Leader, SCG, CMSM, NIMS; Professor, Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo), Takashi Yagi (Group Leader, Thermophysical Property Standards Group, Research Institute for Material and Chemical Measurement, National Institute of Advanced Industrial Science and Technology (AIST)), Junichiro Shiomi (Professor, Institute of Engineering Innovation, School of Engineering, The University of Tokyo), and Daichi Chiba (Professor, SANKEN, the University of Osaka; Director, International Center for Synchrotron Radiation Innovation Smart, Tohoku University). The work was supported by JST ERATO "Uchida Magnetic Thermal Management Materials Project" (Research Director: Ken-ichi Uchida; Grant No.: JPMJER2201), and JSPS Grants-in-Aid for Scientific Research (S) (22H04965) and Grant-in-Aid for Research Activity Start-up (22K20495).
• This research result was published online in Advanced Functional Materials on October 1, 2025.