Synthesis and investigating of the impact of the barium substitution on the structural, magnetic, magnetocaloric effect and critical properties of La0.7Ba0.3-xMn0.95Fe0.05O3 (x=0 and 0.06)

In this current investigation, we have carefully studied the structural, magnetic, magnetocaloric effect and the critical phenomena of the La(0.7)Ba(0.3-x)Mn(0.95)Fe(0.05)O3(x = 0 and 0.06) compounds. The structural study pinpoints that the best structure for the compounds crystallization is the rhombohedral structure with the symmetry of R-3C. The M (T) curves indicated that the compounds exhibit a magnetic transition from the ferromagnetic coupling to the paramagnetic coupling around the Curie temperature Tc. The calculation of Tc with the derivative method gives these values: Tc = 263 +/- 0.5 K and 238 +/- 0.5 K for x = 0 and x = 0.06, respectively. We showed that the experimental effective moment is higher than the theoretical thanks to the presence of some ferromagnetic coupling in the paramagnetic state. The magnetic entropy change as a function of temperature displayed the transition from order to disorder state around the Curie temperature Tc. The several values of -Delta S-M at 5 T applied magnetic field is equal to 2.9 +/- 0.1 J/Kg K and 2.1 +/- 0.1 J/Kg K for x = 0 and 0.06, respectively. One can deduce that our compounds can be as perfect candidates in the magnetic refrigeration especially the parent compound due to the Curie temperature is around to the room temperature. The universal master curves showed that the compound displayed a second order magnetic transition. In the aim to identify the universality class, we turn to study the critical phenomena. Based on Banerjee approach, we confirm again that the compounds exhibit a second order transition. Following the mean field approximation, we determined that the Ising model is the best for the undoped compound and when the barium content decreases, the model would be the tricritical mean field model. We determined the several values of the critical exponents and we showed that are so close to of the theoretical model chosen. We confirm the reliability of the determined exponent values through the scaling theory.