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 R15Si9C (R=Gd, Tb and Dy) compounds which was studied by magnetization and zero field heat capacity measurements. Gd15Si9C, Tb15Si9C and Dy15Si9C undergo ferromagnetic transition below 170K, 130K and 70K respectively. The Arrott’s plot (M2 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 (ΔSM or MCE) and relative cooling power (RCP) for a magnetic field change of 0–70kOe are evaluated to be −12.9J/kgK and 413J/kg for Dy15Si9C, around 70K 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 5.06K, 6.64K and 5.52K for Gd, Tb and Dy compounds respectively at TC for 0→70kOe of field change. The full-width at half-maximum approaches to 85K and 64K respectively for 70kOe of field change for Tb and Dy counterpart. Large reversible MCE and RCP values indicate that R15Si9C are promising materials for magnetic refrigeration in appropriate temperature regions.