Tunable magnetocaloric effect in La0.7Ca0.3MnO3 nanoparticles

We study ferromagnetic to paramagnetic transition using Banerjee criterion in colossal magnetoresistive La0.7Ca0.3MnO3 nanoparticles of different sizes (20, 26 and 32 nm). These particles are chemically prepared by a modified citrate route. Particle sizes are estimated by X-ray diffraction (XRD). Sample morphology and size distribution are examined by a transmission electron microscope. Order of transition is determined by measuring magnetic field dependence of magnetization near Curie temperature T-c. Our results reveal second-order magnetic transition in all three different-sized particles in contrast to the first-order transition reported in bulk samples. This is further supported by temperature dependences of zero-field-cooled (ZFC) and field-cooled (FC) magnetizations. FC curves show gradual transition for all three samples without any saturation region as is the case of bulk. T-c is extracted from ZFC curves and is found to be 240 K for 20 nm particles and 258 K for both 26 and 32 nm particles. Magnetocaloric effect as a function of particle size also confirms the second-order magnetic transition in all three samples. The relative cooling power at 20 kOe is found to be decreasing with decreasing particle size.