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 (T-C). A large magnetocaloric effect is observed near T-C. The maximum value of the magnetic entropy change is Delta SMmax=4.45 for x=0.06. Gallium doping reduces T-C and Delta SMmax. The relative cooling power (RCP) reaches 40Jkg(-1) (resp. 200Jkg(-1)) with 1T (resp. 4.5T) applied magnetic field for La0.65Bi0.05Sr0.3MnO3 manganites. For La0.65Bi0.05Sr0.3Mn0.94Ga0.06O3, the RCP value is 48Jkg(-1) (resp. 220Jkg(-1)) with 1T (resp. 4.5T) 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.