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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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将Nb2O5掺杂到用溶胶-凝胶法制备的La0.67Sr0.33MnO3(LSMO)微粉中,XRD测量结果表明所有样品均为单相菱面结构.随着Nb5 掺杂量的增加,材料电阻率发生显著变化.在x=0.06的掺杂样品中得到最高为1110Ω·cm电阻率(x是掺入的Nb离子与母体材料的摩尔比),比LSMO高5个数量级,这是由于晶界处以及颗粒内部增加的自旋相关的散射和隧穿效应所致.Nb5 离子的掺杂使样品的低场磁电阻(LFMR)和高场磁电阻(HFMR)效应都有所增强.77K下,0.1和1T磁场下在x=0.07样品中分别得到25%和42%的磁电阻效应,分别是LSMO样品的2倍和1.7倍.室温下x=0.03样品的磁电阻最大,为7%.其中,LFMR来源于颗粒晶界处电子的自旋相关隧穿及散射作用,而HFMR来源于表面层的自旋非共线结构. 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