Magnetic and dielectric studies of the La0.8Na0.2Mn0.97Fe0.03O3 sol–gel compound

Abstract

This research aimed to investigate the magnetic and dielectric phenomena of the La_0.8Na_0.2Mn_0.97Fe_0.03O₃ sol–gel compound. Through the magnetic analysis of M (μ₀H, T), we observed that the compound undergoes a ferromagnetic–paramagnetic phase transition. A perfect coincidence was observed between the magnetic entropy changes calculated using the Maxwell relation and Landau theory only in the high-temperature range. Furthermore, based on the mean field theory, we calculate the number of spins (S = 3) and the saturation magnetization (M_sat = 87emu/g). With these parameters, we computed – ΔS_M at different applied magnetic fields. We have observed an appreciable coincidence between -ΔSM calculated using the Maxwell relation and mean field model, confirming the validity of this technique. This suggests that the phase transition of our compound is completely described by the mean field model. Moving forward, we planned to continue investigating of the compound in our study by the critical phenomena. We calculated the critical exponent values using different approaches, such as Kouvel–Fisher, Modified Arrott plot, and critical isotherm technique. The Banerjee approach confirmed that the phase transition is of second order. We determined that the mean field model is the best description for the transition of La_0.8Na_0.2Mn_0.97Fe_0.03O₃. The determined values are β = 0.43, γ = 1.09 and δ = 3.57. Finally, the total conductivity plots for the sample were established by Jonscher power law. The effect of frequency, temperature on the constant dielectric (ε") and the dielectric loss (tan δ) has been deliberated in terms of hopping of the charge carriers between Mn³⁺ and Mn⁴⁺ ions. Activation energy has been calculated from both temperature dependence of the continuous conductivity and the relaxation time values that confirm that same kinds of charge carriers are governing both the processes. Nyquist plot of the impedance displays semicircle arcs and the electrical equivalent circuit of the type of RG + (RGB//CPE) has been proposed to explain the impedance results.

Graphical abstract