【摘要】 系统研究了Mn位替代的La2/3Ca1/3Mn0.9Co0.1O3的电输运特性和磁诱导行为,这里替代Co离子的多价态对应有多重的自旋态变化.发现了存在于Co替代La2/3Ca1/3Mn0.9Co0.1O3电输运行为上的双峰效应,具体表现为除了居里温度Tc附近电阻-温度曲线的金属-绝缘(M-I)转变行为(TMIH约为182K)以外,在低温区域电输运行为出现二次性的类M-I转变现象(TMIL约为124K).通过对外加磁场下输运特性的研究表明,随外加磁场的增加,电阻-温度曲线整体呈现降低行为,即表现为负的磁电阻效应;同时,高温区峰值温度TMIH向高温区移动,这与传统CMR锰氧化物M-I转变特性完全一致;而低温峰值温度TMIL则几乎不变,即TMIL表现出某种磁场无关的特征.结合样品磁特性测量结果,我们发现,除了场冷(FC)和零场冷(ZFC)曲线的分叉现象可能证明Co替代诱导Mn位的磁无序而导致体系出现不均匀的铁磁/反铁磁(FM/AFM)团簇外,在低温峰值温度TMIL附近没有观察到磁性异常变化.对照对Cu和Cr等相关体系的类似研究,证明这种低温二次M-I转变可能与Co替代导致体系的氧缺陷有关.更多还原

【Abstract】 The structure, magnetic and transport properties of the perovskite La2/3Ca1/3Mn1-xCoxO3 (x=0,0.1) have been systematically investigated in this paper. The XRD analysis shows the crystal structure of the samples are good single phase with orthorhombic O′phase. The resistivety of the doped compound exhibits two Metal-Insulator (M-I) transitions—double-peak effect : a sharp peak (TMIH=182K) at high temperature corresponding to paramagnetic-ferromagnetic (PM-FM) transition Tc, and a second peak (TMIL=123K) at lower temperature. Under the external magnetic field, the resistivity of two corresponding peaks reduce to some extent compared with those of zero-field, which indicates the sample performance a negative magnetoresistance effect. It is interesting to find out that the TMIH shift to high temperature but the TMIL be almost unchanged under the external field. Magnetic properties show the formation of ferromagnetic (FM)/antiferromagnetic (AFM)cluster and magnetic disorder in this system induced by Co which has complicated valence and spin states. But no magnetic changing signal could be seen corresponding to the TMIL. Combined with the magnetization properties, it could be concluded that the abnormal behavior of the second M-I transition at the low temperature have some relationship with the oxygen vacancy and the Co-doped intrinsically inhomogeneous system.更多还原