Demagnetizing field-induced magnetocaloric effect in Gd

Abstract

We have studied the impact of demagnetizing fields on the magnetocaloric effect of commercial-grade gadolinium plates. Adiabatic temperature changes ( ? T ) were measured for magnetic fields applied along the parallel and perpendicular directions of the plates. The differences in the obtained ? T values were accounted for by differences in the internal field due to demagnetizing effects. A combination of calorimetric measurements under a magnetic field and thermometric measurements has enabled us to obtain Brayton cycles for the two different magnetic field orientations. It has been found that the refrigerant capacity for a Brayton cycle working at 1.6 T around room temperature reduces from R C = 9.4 to R C = 5.5 J kg - 1 when the demagnetizing factor changes from N D = 0.035 to N D = 0.928 for the parallel and perpendicular configurations, respectively. It has been shown that it is possible to obtain significant demagnetizing field-induced magnetocaloric effects by rotating the sample in a region of a constant applied magnetic field. The refrigerant capacity of a Brayton cycle around room temperature for a 1.6 T constant applied magnetic field is R C = 0.6 J kg - 1 . The feasibility of these demagnetizing field-induced effects has been confirmed by direct thermometric measurements, which reveal adiabatic temperature changes of 1 K when the sample is rotated between the perpendicular and parallel configurations.