Critical Behavior and Landau Theory in Pr0.55Sr0.45-xNaxMnO3 Manganites

Abstract

In this work, we investigated the critical behavior and magnetocaloric effect of Pr_0.55Sr_0.45-xNa_xMnO₃ manganites (x = 0, 0.05 and 0.1) by using critical exponent analysis and Landau theory. The study revealed that the mean-field, 3D-Heisenberg and 3D-XY models are the best for describing the magnetic interactions for x = 0, 0.05 and 0.1 samples, respectively. With increasing sodium content, the magnetic interactions display a striking change from long-range to short-range interactions, which may be ascribed to an increase in Mn⁴⁺ ions concentration and magnetocrystalline anisotropy. Using Landau theory, we have confirmed that the magnetic transition around T_C is of second-order. An agreement was found between the magnetic entropy change values estimated by Landau theory and those obtained using Maxwell relation for a magnetic field equal to 2 T. This confirms the validity of Landau theory to estimate the magnetocaloric effect of Pr_0.55Sr_0.45-xNa_xMnO₃ samples. The small deviation obtained for our samples below T_C can be attributed to the existence of magnetic disorder in the ferromagnetic phase.