Milling effects on the distribution of Curie temperatures and magnetic properties of Ni-doped La0.7Ca0.3MnO3 compounds

A systematic study of the magnetic and magnetocaloric properties around the ferromagnetic-paramagnetic phase transition temperature has been carried out on La0.2Ca0.3Mn1-xNixO3 (x = 0, 0.02, 0.07, 0.10) compounds synthesized by ball milling from oxides and pure Ni. The order of the transition, analyzed by the Banerjee's criterion and the field dependence of the magnetic entropy change, was found to be of second order for all the studied compositions. The existence of small traces of d-MnO2 phase and the distortions produced during the milling process may induce a competition character of the ferromagnetic and the antiferromagnetic interactions at low fields and motivate the existence of a distribution of Curie temperatures. Once the antiferromagnetic contributions are avoided, the parameters of the distribution, the average Curie temperature (T-C) over bar and the broadening of the distribution Delta T-C, have been obtained from the analysis of the approach to saturation curves and the magnetocaloric effect. (C) 2020 Elsevier B.V. All rights reserved.