La-deficient La0.9MnO3 perovskite nanoparticles with different grain size were prepared by sol-gel method. The crystal structure, microstructure, magnetic properties, and magnetocaloric effect in La0.9MnO3 nanoparticles were studied using x-ray diffraction, scanning electron microscopy and vibrating sample magnetom-eter. All samples that annealed at different temperatures (700 ℃~1100 ℃) have rhombohedral structure. With the increase of annealing temperatures from 700 ℃ to 1100 ℃, the average crystal size increases gradually from 25 nm to 1000 nm. The magnetization and magnetic entropy change (ΔSM) increase with the increase of crystal size. The value of ΔSM becomes stable when the crystal size is larger than 500 nm.%采用溶胶-凝胶法制备不同粒径的La缺位La0.9MnO3钙钛矿氧化物.用X射线衍射、扫描电子显微镜、振动样品磁强计对材料的晶体结构、微结构、磁性和磁热效应进行了研究.结果表明，不同温度下退火（700 oC~1100 oC）的样品均具有菱形钙钛矿结构.退火温度从700 oC增加到1100 oC，样品的平均晶粒大小从25 nm增加到1000 nm.随着晶粒大小的增加，材料在低温的饱和磁化强度逐渐增强，铁磁到顺磁的相变变得陡峭，从而使材料的磁熵变逐渐增加.当材料的晶粒尺寸大于500 nm时，材料的磁熵变趋于稳定（-2.7 J/kg·K）.
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