Oscillating Gadolinium Thermal Diode Using Temperature‐Dependent Magnetic Forces
Qing Zhu, Kaitlyn Zdrojewski, Lorenzo Castelli, Geoff Wehmeyer
Abstract
Abstract High‐performance thermal diodes would enable improved waste heat scavenging and thermal management systems. Prior study has indicated that the temperature ( T )‐dependent magnetic response of ferromagnets near the Curie temperature provides a potential mechanism for thermal rectification via thermally induced mechanical oscillations between hot and cold surfaces, but the rectification was not investigated in a macroscopic device. Here, a centimeter‐scale oscillating gadolinium thermal diode (OGTD) is constructed with steady‐state thermal rectification ratios (γ) as large as γ = 23 in air and γ = 16 in vacuum. In the forward mode when the top surface is warmer than 26 °C and the bottom surface is colder than 20 °C, an unstable balance between gravitational forces and T ‐dependent magnetic forces causes a shuttle containing gadolinium to oscillate and transfer thermal energy. In the reverse mode, the shuttle does not oscillate and energy is transferred via parasitic conduction. The diode is durable over >10 3 oscillation cycles and can be used in thermal circuits for rapid thermal regulation in time‐varying environments or half‐wave thermal rectification with up to 50% of the ideal‐diode performance. The experiments show that the OGTD can achieve large γ in a convenient geometry and T range for thermal control applications.