Modulated Magneto-Thermal Response of La_0.85Sr_0.15MnO₃and (Ni_0.6Cu_0.2Zn_0.2)Fe₂O₄Composites for Thermal Energy Harvesters

The magneto-thermoelectric generator (MTG) converts wasted thermal energy into electrical energy in two steps. The first step involves thermal to mechanical energy conversion through balance of magnetic and elastic forces and the second step involves mechanical to electrical energy conversion through piezoelectric effect. The requirements for soft magnetic material in improving the efficiency of first step were identified and met through the design of a composite architecture. The Curie temperature of La(1-x)SrxMnO3 can be engineered to be near room temperature by modifying the Sr content. Composite of La0.85Sr0.15MnO3 (LSMO) and Ni0.6Cu0.2Zn0.2Fe2O4 (NCZF) was found to exhibit high saturation (Ms) and remnant (Mr) magnetization magnitude while maintaining the soft magnetic nature. Two-step sintering was found to prevent the inter-diffusion of LSMO and NCZF phases and provided high density without grain growth. The LSMO-NCZF (70:30 wt%) composite exhibited a large variation in Ms with respect to the change in temperature near Curie temperature which meets the requirements for efficient operation of MTG. The fabricated MTG using LSMO-NCZF (70:30 wt%) composite reached 0.2Hz operational frequency and generated electrical output voltage of 2Vp-p and peak power of 17μW under the thermal gradient of 80°C (0°C/80°C).