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

In this paper, we present a detailed study on the critical behavior around the ferromagnetic (FM)-paramagnetic phase transition in La_1-xK_xMnO₃ (LKMO) compounds with x = 0.05-0.20. Our results pointed out the easiness in controlling the value of TC 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 TC 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 ß 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 (ß and S) depend strongly on K-concentration, shifting from values approaching those of the MFT (ß = 0.5 and σ = 3) to values approaching those of the 3-D-Heisenberg model (ß = 0.365 and σ = 4.80). In contrast, the value of the exponent y (=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.