Structure, magnetism, critical behavior and magnetocaloric effects of La0.66Ca0.33MnO3 porous nanospheres tuned by a solvothermal method with PVP addition

Abstract

La0.66Ca0.33MnO3 porous nanospheres were synthesized by a solvothermal method. The diameter, pore size and density of La0.66Ca0.33MnO3 porous nanospheres were controlled by changing the concentration of PVP (Ployvinylpyrrolidone, K29–32) addition. The effects of structure on the magnetic phase transition, magnetocaloric effects and critical index of the samples were investigated. The results indicated that La0.66Ca0.33MnO3 exhibited a second order paramagnetic (PM)-ferromagnetic (FM) transition. The shorter Mn-O bond length and larger Mn-O-Mn angle of the La0.66Ca0.33MnO3 porous nanospheres enhanced the double exchange, leading to an increase in Curie temperature. The critical parameters β, γ and δ of the samples were confirmed using the modified arrott plot (MAP). The critical parameters of La0.66Ca0.33MnO3 nanospheres without PVP addition were similar to the Mean field model. While the La0.66Ca0.33MnO3 porous nanospheres with PVP addition were judged to favor the Ising model using RS parallelism. The maximum magnetic entropy changes were calculated from the isothermal magnetization curve and observed for -ΔSM(5 T) NPS-0.75 g was 3.994 J/kg.K. NPS-1 g with the highest PVP addition had a large -ΔSM half-height wide temperature interval, obtaining the maximum relative cooling capacity (RCP) of 247.364 J/kg (5 T). These obtained values showed that the La0.66Ca0.33MnO3 porous nanospheres could be as promising candidates for magnetic refrigeration near room temperature.