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A systematic investigation of the magnetic and transport properties of Ti doped La0.67Ca0.33MnO3 was reported. The Ti substitution for Mn ions results in a reduction in ferromagnetism and conductivity. The metal-insulator transition temperature is close to Curie temperature which decreases from 274 to 82 K as x increases from 0 to 0.17. The most important effect of Ti doping is to introduce spin clusters in the samples due to the distortion of local lattice and the inhomogeneous magnetic structure induced primarily by the random distribution of Mn ions. A maximum magnetoresistance ratio as large as 90% in 1 T at 122 K was obtained for the sample with x =0. 055, which is four times larger than that obtained for LCMO sample at 272 K. There is a remarkable field-history dependent MR in the cooling process for the doped samples while such phenomenon disappears in the warming run. The resistivity follows well the variable range hopping behavior in paramagnetic state. Both the size effect and spin dependent hopping of carriers between the spin clusters should be considered in this system. 相似文献
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Multilayered FeSi/Si amorphous films with fixed FeSi layer thickness and different Si layer thicknesses have been studied by conversion electron Mossbauer spectroscopy at room temperature. The results showed that with decreasing the Si layer thickness, the hyperfine field of samples increased and the thickness of interface dead layers arisen from the atomic interdiffusion effect decreased. These are due to the coupling effect between the magnetic layers. When the Si layers are thinner than 0.88 nm, the direction of the magnetization is out of the film plane. 相似文献
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用射频溅射法系统研究了非晶态CoFeNiNbSiB软磁薄膜的制备工艺,发现在0.5Pa的低氩气压下,可以得到性能优良的软磁薄膜,而且膜的性能受衬底偏压影响很小.经旋转磁场退火热处理后,膜的起始磁导率一直到10MHz都可在3000以上,表现出良好的频率特性.用电阻法研究了非晶膜在退火过程中的结构变化过程,发现高温下非晶膜明显经历了四个连续的阶段。 相似文献
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La0.5-xYxBa0.5CoO3 polycrystals were prepared by solid state reaction. The substituting effects of Y for La on the magnetic and transport properties of the materials were studied systematically. The results indicate that substitution of Y induces two effects. Firstly, the charge transfer from Y to 3d orbital of Co happens. This causes the molecular magnetic moment to decrease. Secondly, the antiferromagnetic exchange interaction of Co ions appears. When the content of Y is less than or equal to 30%, the non-colinear structure of spins in materials is observed. When the content of Y is greater than 30%, the materials transit from predominant ferromagnetic state to predominant antiferromagnetic one. The conductive mechanism for the materials with different content of Y belongs to the variable range hopping conduction of polarons.The resistivity of materials increases sharply with increasing Y content. 相似文献
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用固相反应法制备了La0.5-xPrxBa0.5CoO3系列化合物,系统研究了Pr不同含量时材料的磁性和电输运特性,结果表明:Pr掺杂没有改变Co的3d电子的巡游特性。随Pr掺杂量增加,材料的分子磁矩单调下降,其原因是当Pr逐渐取代La时,Co离子的3d电子逐渐由中间自旋态向低自放态转变。随Pr含量增加,材料的居里温度逐渐下降,这是由于稀土离子的尺寸效应,电阻测量表明:在所研究的温度范围内,居里温度以下,所有掺Pr材料的导电机制为热扩散型。居里点以上,导电机制为变程跳跃导电。 相似文献