Rotating magnetocaloric effect in polycrystals-harnessing the demagnetizing effect

Climate change and the increasing demand for energy globally have motivated the search for a more sustainable heat-pumping technology. Magnetic refrigeration stands as one of the most promising alternative technologies for clean and efficient heat pumps of the future. The rotating magnetocaloric effect (RMCE) has previously been studied in materials with magnetocrystalline anisotropy due to its potential to improve devices by requiring only a single magnetic field region, but these materials are fragile and costly to obtain, making them inviable for applications. It has been shown that by exploiting the demagnetizing effect, an RMCE is, in fact, attainable in any polycrystalline magnetocaloric sample with an asymmetric shape, without requiring magnetocrystalline anisotropy. Using gadolinium as a case study, we provide a theoretical framework for computing the demagnetizing field-based RMCE and present thorough experimental verification for different magnetic field intensities and a wide temperature range. Direct measurements of the RMCE in gadolinium reveal that a significant adiabatic temperature difference (1.2 K) and refrigerant capacity (7.44 J kg-1) can be attained within low magnetic field amplitudes (0.4 T). Utilizing lower magnetic field intensities in a magnetocaloric heat pump can significantly diminish the need for permanent magnet materials, thus reducing the overall device cost, size, and weight, ultimately enhancing the feasibility of mass-producing such devices.