Physical properties of Na-doped La0.7Sr0.3MnO3perovskites near the magnetic phase transitions

• Main Authors: Shih-Hong Liou, 劉時宏
• Other Authors: Yung-Kang Kuo
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/33145829932391484510

碩士 === 國立東華大學 === 應用物理研究所 === 94 === We report the investigations of x-ray diffraction, micro-structure, electrical resistivity, magnetization and specific heat on the colossal magnetoresistance (CMR) perovskite samples of La0.7Sr0.3-xNaxMnO3 with x = 0 , 0.03 , 0.07, 0.10. All measured physical properties undergo pronounced anomalies due to the ferromagnetic-paramagnetic phase transition in these compounds. It is found that the metal to insulator transition temperatures TP determined from the electrical resistivity measurements is consistently lower than that of the Curie temperature TC determined from the magnetization measurements. By replacing Sr with Na, both TC and TP initially increase but decrease noticeably with larger x. The decrease in TC at the highest doping level (x =0.10) we investigated is about 15 K, which is considerably smaller than those observed for other elements such as Fe (ΔTC ~ 100 K). It is also found that the entropy change during the phase transition is reduced with increase in Na substitution. These observed results imply that the substitution of Na has the effect of breaking the Mn3+-O-Mn4+ double exchange network and weakening the ferromagnetism to the La0.7Sr0.3MnO3 perovskite.