Thermal Imaging of Thomson and Peltier Effects in Phase Change Materials

The Seebeck and Peltier effects have been widely studied and used in various thermoelectric technologies, including thermal energy harvesting and solid-state heat pumps. However, basic and applied studies on the Thomson effect, another fundamental thermoelectric effect in conductors, are limited despite the fact that the Thomson effect allows electronic cooling through the application of a temperature gradient bias rather than the construction of junction structures [1-3]. In this talk, we mainly report the observation of a giant Thomson effect that appears owing to magnetic phase transitions [4]. The Thomson coefficient of FeRh-based alloys reaches large values approaching -1 mV K^-1 around room temperature because of the steep temperature dependence of the Seebeck coefficient associated with the antiferromagnetic–ferromagnetic phase transition. The Thomson coefficient is several orders of magnitude larger than the Seebeck coefficient of the alloys. Using the lock-in thermography technique, we demonstrate that the Thomson cooling can be much larger than Joule heating in the same material even in a nearly steady state. The operation temperature of the giant Thomson effect in the FeRh-based alloys can be tuned over a wide range by applying an external magnetic field or by slightly changing the composition. This findings provide a new direction in the materials science of thermoelectrics and pave the way for thermal management applications using the Thomson effect.<br/>We also report that the thermal imaging of the Peltier effect by lock-in thermography is a powerful technique for easily visualizing phase boundaries in phase change materials.<br/><br/>[1] K. Uchida, M. Murata, A. Miura, and R. Iguchi, Phys. Rev. Lett. <b>125</b>, 106601 (2020).<br/>[2] R. Modak, T. Hirai, S. Mitani, and K. Uchida, Phys. Rev. Lett. <b>131</b>, 206701 (2023).<br/>[3] T. Chiba, R. Iguchi, T. Komine, Y. Hasegawa, and K. Uchida, Jpn. J. Appl. Phys. <b>62</b>, 037001 (2023).<br/>[4] R. Modak et al., Appl. Phys. Rev. <b>9</b>, 011414 (2022).