Tuning the microstructure and magnetocaloric properties of Na+-substituted La0.67Ca0.33−xNaxMnO3 porous nanospheres

This study investigated the effects of Na + substitution on the microstructure and magnetocaloric properties of La 0.67 Ca 0.33−x Na x MnO 3 (x = 0, 0.05, 0.10, 0.15, 0.20) porous nanospheres synthesized by the solvothermal method. The structural analysis showed that Na + substitution increased the unit cell volume and distorted the lattice structure of La 0.67 Ca 0.33−x Na x MnO 3 porous nanospheres. Na + doping also reduced the diameter uniformity of the porous nanospheres and caused them to relax and disintegrate. The magnetocaloric measurements revealed that Na + doping increased the Curie temperature values. The La 0.67 Ca 0.23 Na 0.1 MnO 3 composition exhibited a maximum magnetic entropy change of 3.57 J/kg.K, while La 0.67 Ca 0.18 Na 0.15 MnO 3 achieved the largest relative cooling power of 308.18 J/kg under an applied field H = 5 T. The critical parameters of the La 0.67 Ca 0.33−x Na x MnO 3 porous nanospheres were examined using the modified Arrott plot, Kouvel-Fisher method and critical isotherm, indicating significant changes in critical parameters due to Na + doping. The results suggested that Na + -substituted La 0.67 Ca 0.33−x Na x MnO 3 porous nanospheres could be promising candidates for magnetic refrigeration near room temperature.