La_(0.67)Sr_(0.33)Fe_xMn_(1-x)O_3制备和奇特磁电阻效应

系列陶瓷氧化物La0.67Sr0.33FexMn1-xO3（0.055x0.33）通过共沉淀法工艺合成获得.经X射线衍射分析表明，所得氧化物均为单相，属三方结构.在零场和外加磁场下的四极法电阻测试结果表明：所有样品都具有较大的磁电阻效应，当x<0.13时，样品的电阻率-温度曲线中均出现电阻率峰（电阻率出现从半导体性向金属性的转变），该电阻率峰处的温度（Tp）随x的增大而向低温区移动，磁电阻效应是负值;x＝0.23时，样品已呈半导体性，磁电阻效应仍是负值;然而x＝0.33时，样品虽也表现为半导体性，但其中的磁电阻效应出现奇特的正负交替转换.

Preparation and Peculiar Magnetoresistance of Ln_(0.67)Sr_(0.33)Fe_xMn_(1-x)O_3

The Ln0.67Sr0.33Fe.Mn1-xO3(LSFMO)(0.05< x <0.33) systerns have been synthesized by co-precipitation. The X-ray diffraction patterns indicates that these conrpounds are of single phase with rhombohedral structure. The resistivity of samples was measured in zero field and applied field (H=4000Oe) by a standard four-probe method- Large magnetoresistance (MR) was found in all samples. There is a resistivity transition peak in LSFMO (x <0.13) in which MR negative, the temperature (TP) at which the resistivity peak occurs decreases with the increasing of x. LSFMO (x=o.23) to which the large negative MR is stin found is a sendconductor, It is unexpected that a peculfor alternative positive negative MR was found in LSFMO(x=0.33) which also is a semicondutor.