Abstract
The critical behaviour and magnetic field dependence of magnetic entropy changes (Delta S-M) for the ferromagnetic La0.65Nd0.05Ba0.3Mn1-xCrxO3 (0 <= x <= 0.15) ceramics are systematically investigated in details. Upon Cr doping, the Curie temperature T-C, Delta S-M and the critical exponents (beta, gamma, and delta) are substantially influenced. As a result, the T-C varies from 330 K for x = 0 to 275 K for x = 0.15 and the Delta S-M decreases gradually with higher Cr substitution. The values of the critical exponents of the prepared samples lie between the Tricritical mean field model and 3D-Ising model. Thus, these results suggest that critical phenomena in La0.65Nd0.05Ba0.3Mn1-xCrxO3 (0 <= x <= 0.15) could not be explained on the conventional universality classes. However, the obtained results suggest an existence of FM short-range order in the prepared samples. To check the agreement with the scaling theory, m = f +/- (h) is plotted for all samples. It was found that all data points fall into two separate branches above and below the critical temperature, T-C, which confirmed that the critical exponents are reliable. The analysis of the field dependence of the Delta S-M reveals the power law dependence at the transition temperature. Based on the value of critical exponents, one can find that all the magnetic entropy changes and heat capacity changes fall on a master curve for all measured fields and temperatures confirming the nature of second-order magnetic transition. This excellent overlap clearly indicates that the critical exponents obtained for the prepared system are reasonably accurate.