Tuning the magnetocaloric properties of La0.7Ca0.3MnO3 manganites through Ni-doping.

The effect of Ni 2+ doping on the magnetic and magnetocaloric properties of La 0.7 Ca 0.3 MnO 3 manganites synthesized via the auto-combustion method is reported. The aim of studying Ni 2+ -substituted La 0.7 Ca 0.3 Mn 1 − x Ni x O 3 ( x = 0 , 0.02 , 0.07 , and 0.1) manganites was to explore the possibility of increasing the operating temperature range for the magnetocaloric effect through tuning of the magnetic transition temperature. X-ray diffraction analysis confirmed the phase purity of the synthesized samples. The substitution of Mn 3+ ions by Ni 2+ ions in the La 0.7 Ca 0.3 MnO 3 lattice was also corroborated through this technique. The dependence of the magnetization on the temperature reveals that all the compositions exhibit a well-defined ferromagnetic to paramagnetic transition near the Curie temperature. A systematic decrease in the values of the Curie temperature is clearly observed upon Ni 2+ doping. Probably the replacement of Mn 3+ by Ni 2+ ions in the La 0.7 Ca 0.3 MnO 3 lattice weakens the Mn 3+ –O–Mn 4+ double exchange interaction, which leads to a decrease in the transition temperature and the magnetic moment in the samples. By using Arrott plots, it was found that the phase transition from ferromagnetic to paramagnetic is second order. The maximum magnetic entropy changes observed for the x = 0 , 0.02 , 0.07 , and 0.1 composites was 0.85, 0.77, 0.63, and 0.59 J/kg K, respectively, under a magnetic field of 1.5 T. In general, it was verified that the magnetic entropy change achieved for La 0.7 Ca 0.3 Mn 1 − x Ni x O 3 manganites synthesized via the auto-combustion method is higher than those reported for other manganites with comparable Ni 2+ -doping levels synthesized via standard solid state reaction. The addition of Ni 2+ increases the value of the relative cooling power as compared to that of the parent compound. The highest value of this parameter (∼60 J/kg) is found for a Ni-doping level of 2% around 230 K in a field of 1.5 T. [ABSTRACT FROM AUTHOR]