Waste heat is a growing and abundant energy resource, particularly at low temperature below 200°C, which is difficult to recover by existing energy conversion technologies. Progress in the development of films that exhibit large abrupt changes in magnetization and rapid heat transfer unclose the development of thermodynamically efficient thermomagnetic generators. Detailed experiments and lumped element simulations for the case of Heusler alloy film Ni-Mn-Ga show that scaling of film thickness and device footprint oppositely affect power output. Based on this understanding, we could increase the electrical power per footprint by a factor of 3.4 for increasing film thickness from 5 to 40 μm reaching values of 50 μW/cm2 at a temperature change of only 3°C. These results pave the way for the development of advanced generators consisting of parallel architectures with tailored footprint and films operating well below 100°C that open up waste heat recovery near room temperature.
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