Magnetocaloric effect near the second order ferromagnetic transition in superstructure R15Si9C compounds (R=Gd, Tb and Dy)

Abstract Large magnetocaloric effect (MCE) has been observed in R 15 Si 9 C (R = Gd, Tb and Dy) compounds which was studied by magnetization and zero field heat capacity measurements. Gd 15 Si 9 C, Tb 15 Si 9 C and Dy 15 Si 9 C undergo ferromagnetic transition below 170 K, 130 K and 70 K respectively. The Arrott’s plot ( M 2 vs. H / M plot) of the magnetization data and the heat capacity measurement indicate the magnetic transition to be second order in nature. Among Gd, Tb and Dy compounds the maximum value of magnetic entropy change ( Δ S M or MCE) and relative cooling power (RCP) for a magnetic field change of 0–70 kOe are evaluated to be −12.9 J/kg K and 413 J/kg for Dy 15 Si 9 C, around 70 K with no hysteresis loss. The isostructural Gd and Tb compounds also exhibit large values of MCE and RCP around their respectively magnetic transition region. The value of adiabatic temperature change is found to be 5.06 K, 6.64 K and 5.52 K for Gd, Tb and Dy compounds respectively at T C for 0 → 70 kOe of field change. The full-width at half-maximum approaches to 85 K and 64 K respectively for 70 kOe of field change for Tb and Dy counterpart. Large reversible MCE and RCP values indicate that R 15 Si 9 C are promising materials for magnetic refrigeration in appropriate temperature regions.