Critical phenomena in the double-exchange ferromagnet La0.8Na0.2Mn1-xNixO3 around the critical temperature

The research results of magnetocaloric effect and critical properties of La0.8Na0.2Mn1-xNixO3 (0 ≤ x ≤ 0.06) manganite are reported. Using the Banerjee's criteria, Franco method and Landau theory, we proved the second order ferromagnetic-paramagnetic phase transition for all samples. The critical exponents values β, γ and δ are determined using modified Arrott plot (MAP), Kouvel Fisher technique and the critical isotherm. Indeed, comparing our determined exponent values with those of standards model, there is a shifting tendency from the mean field model for the compositions La0.8Na0.2MnO3 and La0.8Na0.2Mn0.97Ni0.03O3 to those of the 3D-Ising model for La0.8Na0.2Mn0.94Ni0.06O3 sample. Thus, reflect that the magnetic coupling tends to change from the long-range to the short-range interaction as increasing Ni content. Particularly, by performing the Landau theory we suggest that the magnetoelastic contribution and the electron interaction should be associated with the Jahn Teller interaction in the determination of ΔSM magnetic entropy change effect in our compounds.