微观结构对溶胶-凝胶法合成的La_(0.67)Sr_(0.33)MnO_3电磁性能影响

Effect of Microstructure on Electric and Magnetic Properties of La_(0.67)Sr_(0.33)MnO_3 Prepared by Sol-Gel Route

采用溶胶-凝胶法制备了不同烧结温度的钙钛矿类锰氧化物La0.67Sr0.33MnO3样品。实验结果表明,在1573 K以上烧结的样品,晶粒出现异常长大,晶界效应明显。随着烧结温度的提高,磁化强度逐渐增大,但样品的居里温度基本不变。此外,在1173和1573 K温度下烧结的样品,均出现了低于居里温度的金属-半导体导电行为转变。在合适的烧结条件下,可以观察到隧道磁电阻(TMR)和超大磁电阻(CMR)2种磁电阻效应。实验表明,自旋电子的输运,不仅与样品平均粒径的大小和密度有关,而且与晶界的微观结构有密切关系。

A series of La0.67Sr0.33MnO3 perovskite oxides was prepared by the sol-gel method. The grain sizes increase abnormally and the grain boundary effects are very prominent for the samples sintered at above 1 573 K. The magnetic strength increases with the sintering temperature. However, the Curie temperatures of all the samples keep constant. The metal-semiconductor behavior can be observed for the samples sintered at 1 173 K and 1 573 K. At proper sintering temperature, both tunneling magnetoresistance（TMR） and colossal magnetoresistance（CMR） can be observed. It indicates the transport of spintronics is related not only to the particle size and the density of the sample, but also to the microstructure of grain boundary.