Structural, magnetic, magnetocaloric and critical studies of Sm-substituted La0.67-xSmxPb0.13Ca0.2MnO3 perovskite manganites

The structural, magnetic, magnetocaloric, and critical behaviors for Sm substituted La0.67-xSmxPb0.13Ca0.2MnO3 manganites with x = 0, 0.1, and 0.2 were investigated in this work. Based on Rietveld refinement of XRD patterns, all samples have an orthorhombic structure with the Pnma space group. With Sm substitution, the average ionic radii of A-site cation (< rA >), the unit cell volume (V), the Goldschmidt tolerance factor (tG), and the average < OMn-O-Mn > bond angle decrease. Whereas the average bond distance, < dMn-O >, and the variance disorder parameter (o2) increase. Ferromagnetic (FM) to paramagnetic (PM) phase transitions with second-order type were revealed for all samples from magnetization measurements and Arrott plots. Curie temperature (TC) decreases with Sm substitution from 298 K for x = 0-256 K for x = 0.2. Large maximum entropy change and relative cooling power (6.20 J Kg-1 K- 1 and 236 J Kg- 1, respectively) have been observed for the undoped sample (x = 0), but the values of these parameters are suppressed due to the disorder caused by Sm doping. The estimated critical exponents (8, y, and 6) for the x = 0 sample are consistent with tricritical mean-field theory. However, for x = 0.1 and 0.2, they are close to the 3D- Ising model. The change in this universality class can be associated with the increase of disorder by substituting the Sm3+ cations in La0.67-xSmxPb0.13Ca0.2MnO3 manganites.