Magnetocaloric Effect and Electron Paramagnetic Resonance Study of Gallium-Doped La0.65Bi0.05Sr0.3Mn1−xGaxO3 (x = 0 and 0.06) Manganites

We have investigated gallium doping effect on magnetic and magnetocaloric properties of La0.65Bi0.05Sr0.3Mn1−xGaxO3 (x = 0 and 0.06) manganites. All compounds present a ferromagnetic–paramagnetic transition at Curie temperature (TC). A large magnetocaloric effect is observed near TC. The maximum value of the magnetic entropy change is ΔSMmax=4.45Jkg-1k-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \Delta S_{\rm{M}}^{\rm{max} } = 4.45\;{\text{J}}\;{\text{kg}}^{ - 1} \;{\text{k}}^{ - 1} $$\end{document} at 4.5 T applied magnetic field for x = 0 compound which decreases to a lower value of ΔSMmax=3.44Jkg-1k-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \Delta S_{\rm{M}}^{\rm{max} } = 3.44\;{\text{J}}\;{\text{kg}}^{ - 1} \;{\text{k}}^{ - 1} $$\end{document} at 4.5 T for x = 0.06. Gallium doping reduces TC and ΔSMmax\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \Delta S_{\rm{M}}^{\rm{max} } $$\end{document}. The relative cooling power (RCP) reaches 40 J kg−1 (resp. 200 J kg−1) with 1 T (resp. 4.5 T) applied magnetic field for La0.65Bi0.05Sr0.3MnO3 manganites. For La0.65Bi0.05Sr0.3Mn0.94Ga0.06O3, the RCP value is 48 J kg−1 (resp. 220 J kg−1) with 1 T (resp. 4.5 T) applied magnetic field. These values are relatively high as compared with those generally reported for manganite, and our samples can be considered as a promising material to be used in ecologically friendly magnetic refrigeration technology. Obviously, the variations of EPR, as the Ga doping increases, giving a further confirmation for the decrease in the Curie temperature, were already observed in analogous magnetic results M(T) curves.