Particle size effects on La0.7Ca0.3MnO3: Griffiths phase-like behavior and magnetocaloric study

We report the particle size effects on the magnetic and magneto caloric properties of La0.7Ca0.3MnO3 nanoparticles. Raw samples, prepared by the reactive milling method, were annealed at different temperatures to produce samples with particle sizes of 21, 35 and 43 nm. The Curie temperature was found to decrease with increasing of grain size. The decrease in saturation magnetization was attributed to weakening of exchange interaction at the surface of the smaller particles. The existence of so-called Griffiths singularity above Curie temperature has been confirmed from non-Curiee Weiss behavior in samples. The magnetic entropy change was calculated by the phenomenological method using the experimental data of magnetization versus temperature. The maximum value of the magnetic entropy increased with increasing of grain size from 2.56 J/kg K for 21 nm sample to 2.68 J/kg K for 43 nm sample upon 6 T applied field change. Finally, the fact that the magnetic entropy change curves at different applied fields are collapsed onto a universal curve proves that the studied manganite undergoes a second order magnetic phase transition. (C) 2015 Elsevier B.V. All rights reserved.