Effect of polymer coating on magnetocaloric properties of garnet

Abstract In this study, Gd 3 Fe 5 O 12 nanoparticles were synthesized using the sol–gel autocombustion method and subsequently coated with polyvinylpyrrolidone (PVP) polymer. The study focuses on understanding the influence of PVP coating on garnet particles’ magnetic and magnetocaloric properties. The crystallite size upon PVP-coating remained unaltered, but the grain size and surface area of coated particles increased. The magnetization of PVP-coated particles decreased by around 11% as compared to the uncoated particles at 5 K. Mössbauer and photoelectron spectroscopy confirmed the presence of a paramagnetic phase Fe 3+ in the PVP-coated nanoparticles responsible for the reduction in magnetization value. The maximum value of magnetic entropy change (−ΔS m ) for uncoated Gd 3 Fe 5 O 12 was 3.78 Jkg −1 K −1 at 37.5 K with a 5T applied field, accompanied by a relative cooling power (RCP) of 382 Jkg −1 . On the other hand, for PVP-coated Gd 3 Fe 5 O 12 , the maximum −ΔS m was 3.38 Jkg −1 K −1 at 57.5 K with a 5T applied field, and the RCP was 308 Jkg −1 . The observed maximum magnetic entropy changes at higher temperatures for the PVP-coated Gd 3 Fe 5 O 12 sample are noteworthy. This characteristic indicates that the PVP-coated garnet may have an advantage in terms of usability over a wider temperature range compared to the uncoated counterpart, which can potentially be a promising material for applications in cryogenic temperature magnetic refrigeration.