择优掺杂的La-Ca-Na-Mn-O体系的庞磁电阻效应

利用溶胶-凝胶法制备出择优掺杂的名义组分为La_(1-x)(Ca_(1-y)Na_y)_xMnO_3(LCNM)的多晶样品.xRD测试表明样品均为钙钛矿结构.电输运测试表明所有样品均发生金属-绝缘体转变和顺磁一铁磁转变(转变温度分别用T_m和T_c表示),转变温度随Na含量的增加而增加,但是由于Ca,Na离子间价态的不同引起的磁不均匀性,同时含Ca和Na的样品电输运曲线在T_m温度以下出现肩型鼓包,同时表现出增宽的顺磁·铁磁转变过程,磁电阻测量发现所有样品均表现出庞磁电阻(CMR)效应,但是由于磁不均匀性,y约为0.25的样品表现出两个CMR峰.

Colossal Magnetoresistance in Optimized-Doped La-Ca-Na-Mn-O System

Optimized-doped polycrystalline samples with nominal composition La_(1-x)(Ca_(1-y)Na_y)_xMnO_3 were synthesized through sol-gel method. The X-ray diffraction result indicated that all samples were single phase with perovskite structure. All samples showed metal-insulator (M-I) transition at the transition tem-perature T_m and under went the transition from para-magnetism to ferromagnetism at the Curie temperature T_c. The T_m and Tc increased monotonically with in-creasing Na content. However, the Na-doped samples had a shoulder in their electrical transport curves be-low T_m and showed a widened magnetic transition process. Especially, samples with y around 0.25 showed two CMR peaks which could be attributed to the strong magnetic competition caused by the magnet-ic inhomogeneity due to the different valence between Ca~(2+) and Na~+.