Glassy ferromagnetism in La0.75Sr0.25-xKxCoO3 polycrystalline perovskite cobaltites

In this paper, the structural and magnetic properties of La0.75Sr0.25-xKxCoO3 (0≤x≤0.15) powder samples are reported. X-ray diffraction analysis using Rietveld refinement show that all our samples crystallize in the rhombohedral structure with R3¯c\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ R\overline{3}c $$\end{document} space group. At low temperatures, with increasing K amount, the samples change from ferromagnetic like behavior (x = 0, 0.05 and 0.1) to spin glass one (x = 0.15). The ferromagnetic-paramagnetic transition temperature decreases with increasing K amount from 235K (x = 0) to 200K (x = 0.1). In the paramagnetic phase, all our synthesized samples obey the Curie-Weiss law. In the vicinity of TC, the magnetic entropy change |ΔSM| for La0.75Sr0.2K0.05CoO3 sample reached maximum values of 0.47Jkg/K and 2.27Jkg/K under magnetic field variation in the range 1T and 7T, respectively. The magnetization hysteresis loops demonstrate a weakening the ferromagnetism with increasing K content.