Pr_(0.5)Sr_(0.5)MnO_3的尺寸效应与低场磁热效应

The Size Effect and Magnetocaloric Effect in Pr_(0.5)Sr_(0.5)MnO_3

采用溶胶凝胶法制备了系列Pr0.5Sr0.5MnO3纳米晶样品,用X射线衍射仪和扫描电子显微镜观察了材料的晶体结构和微结构,并用振动样品磁强计对其磁性和磁热效应进行了研究.结果表明,随着烧结温度的提高,材料颗粒尺寸也相应增大.当材料颗粒尺寸大于115nm时,材料表现出反铁磁到铁磁的一级相变和铁磁到顺磁的二级相变,而当颗粒尺寸小于115nm时,样品低温的反铁磁到铁磁相变消失,只剩下铁磁到顺磁一个相变.采用Maxell关系计算了材料在1T磁场下的磁熵变,在反铁磁到铁磁相变附近发现了正磁熵变,而在铁磁到顺磁相变附近具有负磁熵变.

Pr0.5Sr0.5MnO3 polycrystalline compounds were prepared by sol-gel method, and their properties were investigated by x-ray diffraction, scanning electron microscope, and vibrating sample magnetometer. It was found that the grain size increased with the increase of sintering temperature. When the grain size is larger than 115 nm, the material exhibits an antiferromagnetic to ferromagnetic transition and a ferromagnetic to paramagnet- ic transition. When the grain size is less than 115 nm, the low-temperature antiferromagnetic to ferromagnetic transition disappears, and only ferromagnetic to the paramagnetic transition can be observed. The magnetic entro- py changes were calculated by Maxell relation. A positive magnetic entropy change was found in the antiferro-magnetic to ferromagnetic transition, while a negative magnetic entropy change was observed in the ferromagnetic to the paramagnetic transition.