Magnetic and magnetocaloric properties in Ba-doped La0.7Ca0.3MnO3 nanoparticles

La0.7Ca0.3-xBaxMnO3 nanoparticles with the crystalline size d = 38 and 39 nm for x = 0.025, and 0.05, respectively, were synthesized by utilizing the solid-state reaction and mechanical ball milling methods. We have used the Banerjee's criteria, the mean-field, and the thermodynamic theories, and isothermal magnetization, M(H), data around Curie temperature (T-C) to investigate the magnetic phase transformation and the temperature (T) and magnetic field (H) dependences of magnetic entropy change, Delta S-m(T, H), for nanoparticles. These exhibit the samples undergoing a second-order magnetic phase transition with an existence of the short-range ferromagnetic order in the samples. Under an applied magnetic field change Delta H = 30 kOe, the maximum value of Delta S-m (denoted as vertical bar Delta S-max vertical bar) are obtained about 4.4 J kg(-1) K-1 corresponding to a relative cooling power (RCP) value about 140 J kg(-1). Field dependences of vertical bar Delta S-max vertical bar and RCP can be expressed by the power laws, vertical bar Delta S-max vertical bar = a x H-n and RCP = b x H-N, where a and b are coefficients, n and N are the field exponents, respectively. Interestingly, all the Delta S-m(T, H) curves measured at different applied fields are collapsed onto a universal curve, Delta S-m(T, H)/Delta S-max versus theta = (T - T-C)/(T-r - T-C), where Tr is the reference temperature. (C) 2015 Elsevier B.V. All rights reserved.