Lock-In Thermography as a Tool for Investigating Caloric Effects

Thermal measurement techniques play an important role in pioneering new thermal management principles. We have investigated various physical phenomena and heat control functionalities through active thermal measurement techniques based on the combination of non-contact temperature measurements and lock-in detection. Specifically, we have mainly used the lock-in thermography (LIT) method, in which thermal images are acquired by an infrared camera while periodically applying thermal excitation to a sample. In the LIT method, only the temperature change components that follow the periodic excitation are selectively extracted by Fourier analysis, which makes it easy to achieve highly sensitive temperature measurements with sub-mK-order resolution. There are various choices of excitation sources, such as a charge current, heat current, magnetic field, and light, and a variety of heat generation phenomena responding to the excitation sources can be precisely measured. The main application of the LIT technique has been nondestructive failure analysis of semiconductor devices, since the path of a charge current can be visualized by measuring Joule heating distribution associated with periodic current application. Recently, it has been used for fundamental studies on spin caloritronics and thermoelectrics [1-4].<br/>In this talk, we will summarize the measurement principles and features of the LIT method and present recent experimental results on magnetocaloric [5,6], electrocaloric [7], and elastocaloric [8] effects obtained by this technique. The LIT method not only enables non-contact, simultaneous measurements of adiabatic temperature changes induced by the caloric effects for a large number of samples, but also leads to the demonstration of their new functionalities. This technique will thus be useful for material exploration and application research of the caloric effects.<br/><br/>References:<br/>[1] S. Daimon, R. Iguchi, T. Hioki, E. Saitoh, and K. Uchida, Nature Commun. <b>7</b>, 13754 (2016).<br/>[2] K. Uchida, S. Daimon, R. Iguchi, and E. Saitoh, Nature <b>558</b>, 95 (2018).<br/>[3] J. Wang, Y. K. Takahashi, and K. Uchida, Nature Commun. <b>11</b>, 2 (2020).<br/>[4] K. Uchida, M. Murata, A. Miura, and R. Iguchi, Phys. Rev. Lett. <b>125</b>, 106601 (2020).<br/>[5] Y. Hirayama, R. Iguchi, X.-F. Miao, K. Hono, and K. Uchida, Appl. Phys. Lett. <b>111</b>, 163901 (2017).<br/>[6] R. Modak, R. Iguchi, H. Sepehri-Amin, A. Miura, and K. Uchida, AIP Adv. <b>10</b>, 065005 (2020).<br/>[7] R. Iguchi, D. Fukuda, J. Kano, T. Teranishi, and K. Uchida, arXiv:2209.05385<br/>[8] T. Hirai, R. Iguchi, A. Miura, and K. Uchida, Adv. Funct. Mater. <b>32</b>, 2201116 (2022).