Modeling of magnetic and magnetocaloric properties by the molecular mean field theory in La0.8Ca0.2MnO3 oxides with first and second magnetic phase transition

Magnetic and magnetocaloric properties of La0.8Ca0.2MnO3 manganese oxides has been analyzed based on the mean-field theory. The Bean-Rodbell equation of state shows a second and first order magnetic phase transition for the sample annealed at 1200 degrees C (S-1) and 800 degrees C (S-2) with a eta factor of eta=0.6 and eta=1.4 respectively. Using the experimental data of magnetization M (H,T), the molecular mean-field parameter are found to be lambda(1 )= 0.6564 T g eum(-1) and lambda(1) = 0.8876 T g eum(-1) for S-1 a S-2 respectively. Brillouin function allows us to determine the total angular moment J, the saturation magnetization M-s and the Lande factor g for all samples. Knowing all these parameters, and by applying the mean-field theory, we simulated the magnetization as a function of the magnetic field and the temperature, as well as the variation of the magnetic entropy change Delta S-M(T). We can see that the simulated results are in good agreement with experimental data.