Magnetic properties and magnetocaloric effect of La0.8Ca0.2MnO3 nanoparticles tuned by particle size

La0.8Ca0.2MnO3 particles with the sizes from 17 to 43 nm have been prepared using the sol-gel method and the magnetic properties are systematically studied. The existence of the blocking of the superparamagnetism (SPM), freezing of super-spin-glass, and surface-spin-glass is evidenced. It is found that a core-shell structure can be responsible for the magnetism behavior of the nanoparticles. The phase transition from paramagnetism (PM) to ferromagnetism (FM) is modified from first order to second order as the particle size reduced. The magnetocaloric effect (MCE) thus is modified by the changed magnetism. The observed temperature interval of the magnetic entropy change broadens as the particle size reduced. The magnetic entropy change of superparamagnetic particles has been calculated based on the core-shell model. The relative cooling power (RCP) can be tuned dramatically by particle size due to the change of spontaneous magnetization of the core and the changed ratio of the shell and surface, which shows different behavior in magnetization.