A Coexistence of Short- and Long-Range Ferromagnetic Interactions in La1–xKxMnO3 Compounds

Abstract

In this paper, we present a detailed study on the critical behavior around the ferromagnetic (FM)–paramagnetic phase transition in La1− x K x MnO3 (LKMO) compounds with $x = 0.05 - 0.20$ . Our results pointed out the easiness in controlling the value of $T_{C}$ from 212 to 306 K by increasing K-doping concentration (x) from 0.05 to 0.20. Analyzing temperature and magnetic field dependences of magnetization M(T, H) at temperatures around $T_{C}$ reveals all the samples undergoing the second-order phase transition. Using the modified Arrott plots, the Kouvel–Fisher, and the critical isotherm analysis methods, we have found that the values of exponent $\beta $ in the range of 0.435–0.493, which deviate from the mean-field theory (MFT) for the long-range FM interactions, indicating a coexistence of short- and long-range FM orders. We also pointed out that the critical exponents ( $\beta $ and $\delta)$ depend strongly on K-concentration, shifting from values approaching those of the MFT ( $\beta = 0.5$ and $\delta = 3$ ) to values approaching those of the 3-D-Heisenberg model ( $\beta = 0.365$ and $\delta = 4.80$ ). In contrast, the value of the exponent $\gamma (=1.222 - 1.249)$ is almost independent of K-concentration. It suggests that K-doping favors establishing a short-range FM order in LKMO compounds.