A Near-Field Tunable Magnetocaloric Thermal Switch

The magnetocaloric effect is the phenomenon in which some magnetic materials experience a change in temperature upon an adiabatic change in magnetization. It is well-known that this process can be exploited to achieve magnetic refrigeration and has other potential applications including drug delivery (particularly controlled release) and hyperthermia to treat cancer [1]. In recent years, there has also been an interest in using magnetic fields to manipulate radiative heat transfer, especially in the near-field, where length scales are approximately less than the peak wavelength of the blackbody spectrum and evanescent modes dominate. For example, it is possible to tune the near-field radiative heat transfer between planar doped semiconductors by applying a magnetic field and modulating its magnitude and direction [2]. This is because the applied magnetic field induces off-diagonal elements in the dielectric tensor, which are linked to nonreciprocal modes and magneto-optic effects, as well as uniaxial or biaxial anisotropy, which can give rise to hyperbolic modes. In this work, we have combined the magnetocaloric effect and magnetic control of radiative heat transfer to model a near-field tunable magnetocaloric thermal switch. We have shown that the heat flux between a magnetocaloric material and a magneto-optic material can be controlled via two mechanisms: the temperature change originating from the magnetocaloric effect; and modes such as surface plasmon polaritons and hyperbolic modes that depend on both the magnitude and the direction of the applied magnetic field. Thus, we predict the applied magnetic field enables control over the directionality of the heat flux—from the magnetocaloric material to the magneto-optic material and vice-versa—and its magnitude, both spectrally and totally. Our work points toward a new class of thermal switches with a potentially wide range of operating temperatures dependent on the Curie temperature of the magnetocaloric material. This work is supported by an ARO MURI (Grant No. W911NF-19-1-0279) via the University of Michigan.<br/><br/><b>References</b><br/>[1] A. M. Tishin, Y. I. Spichkin, Int. J. Refrig. 37, 223 (2014).<br/>[2] E. Moncada-Villa, V. Fernández-Hurtado, F. J. García-Vidal, A. García-Martín, J. C. Cuevas, Phys. Rev. B 92, 125418 (2015).