Rotating magnetocaloric effect in polycrystals – harnessing the demagnetizing effect

Abstract

Climate change and the increasing demand for energy globally has 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. Materials with a rotating magnetocaloric effect (RMCE) based on magnetocrystalline anisotropy have previously been explored as refrigerants with the potential to drastically improve device design by requiring a single magnetic field region. It has been shown previously that by exploiting the demagnetizing effect, an RMCE is in fact attainable in any polycrystalline magnetocaloric sample with an asymetric shape, without requiring magnetocrystalline anisotropy. Using gadolinium as a case study, we provide a theoretical framework for computing the demagnetizing field-induced RMCE indirectly, 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) are attained within low magnetic field amplitudes (0.4 T). By employing low field intensities in a magnetocaloric heat pump, the amount of permanent magnet material can be drastically reduced, lowering the overall weight and cost, making devices more viable for mass production.