Eu/Ni doping on the structure, magnetocaloric effect and critical behaviour of La0.65Sr0.35MnO3 ceramics

Magnetic refrigeration (MR) technology possesses the potential to substitute conventional gas compression technology. It is necessary to find MR materials suitable for a variety of applications. In this study, La0.65Sr0.35-xEuxMn0.95Ni0.05O3 (x = 0.05, 0.075, 0.10) (LSExMNO) ceramics were prepared using a sol-gel synthesis process. The LSExMNO ceramics were confirmed to be the R‾3c space group (rhombohedral structure) by X-ray diffraction (XRD) analysis. The particles of LSExMNO ceramic particles were irregular polyhedral particles by Scanning electron microscopy (SEM). The chemical composition of LSExMNO was determined by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The Magnetic Property Measurement System (MPMS) demonstrated that the LSExMNO ceramics display second-order magnetic phase transitions (SOMPT) around Curie temperature (TC). When the Eu3+ doping level increased, the Mn–O–Mn bond angle and length increased, weakening the exchange coupling of the Mn4+-O2--Mn3+ channel and decreasing the TC. As the amount of Eu3+ doping varied, the maximum magnetic entropy (–ΔSMMax) of the LSExMNO ceramics peaked at 4.03 J kg−1K−1 and cooling efficiency parameter (RCP) = 291.2 J kg−1 at x = 0.075. The Modified Arrott plots (MAP) and Kouvel-Fisher (K–F) approaches were applied for the purpose of certifying the critical exponents of LSE0.075MNO ceramics conform to the Mean Filed model. Compared with other magnetic materials, it displays an excellent magnetocaloric effect (MCE) with a TC of 299 K.