Magnetic phase transitions and magnetocaloric effect in La0.7Ca0.3Mn1-xFexO3 0.00 ≤ x ≤ 0.07 manganites

We report a systematic study of the magnetic and magnetocaloric properties of La0.7Ca0.3Mn1-xFexO3, where trivalent Fe is substituted for Mn on the perovskite B-site in the doping range 0.00 <= x <= 0.07. The polycrystalline materials were prepared by a standard solid state reaction method and X-ray diffraction confirmed that Fe was incorporated without significant structural changes. Magnetic measurements indicate that the ferromagnetic double exchange interaction is weakened with increasing Fe concentration, resulting in a shift in T-C from 263K to 114K as x varied between 0.00 and 0.07. The large entropy change of 7.7 J/kg K found in the sample with x = 0 for a field change of 3 T is initially enhanced to 8.6 J/kg K for x = 0.01, which is likely due to oxygen deficiency. As Fe content increased further, peak entropy values were seen to decline. However, a simultaneous broadening of the Delta S-M(T) peaks led to enhanced refrigerant capacity (RC) in the Fe-doped samples of up to 30% over that of La0.7Ca0.3MnO3. Arrott plot analyses and a universal curve method were applied to study the order of the magnetic transition in this system. The incorporation of Fe led to a weakening of first-order nature of the paramagnetic to ferromagnetic transition in La0.7Ca0.3MnO3 and finally initiated a change from first to second order for x>0.05. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768175]