Electrical Resistivity and Magnetoresistance in Monodispersed Oxide-Coated Fe Cluster Assemblies
Electrical Resistivity and Magnetoresistance in Monodispersed Oxide-Coated Fe Cluster Assemblies
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DOI：
10.1143/jjap.43.674
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发表时间：
2004-02
影响因子：
1.5
通讯作者：
D. Peng;T. Hihara;K. Sumiyama
中科院分区：
文献类型：
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作者：
D. Peng;T. Hihara;K. Sumiyama
我们系统地研究了由等离子体-气体-凝聚型团簇束沉积系统制备的平均团簇尺寸为d = 9-17 nm的尺寸单分散氧化物包覆的Fe团簇组装体的电阻率和磁电阻（MR）。电阻率和磁阻强烈地依赖于温度、团簇的表面氧化程度（即O2气体流量比RO 2）、Fe团簇尺寸d和磁场。的氧化物涂层的Fe簇组装体表现出大的负MR效应，这是进一步增强，在低温下，由于占主导地位的贡献的自旋相关的铁核之间的隧穿过程通过氧化物壳层。已经发现，在所有温度下的MR比的磁场依赖性显示没有饱和趋势，直到最大场H = 50 kOe和完全不同意的磁化曲线，表明饱和趋势。这些结果已被解释考虑的铁氧化物壳层的磁性状态，自旋相关的隧道机制，和团簇间的磁关联。高场非饱和行为的磁阻效应是由于自旋无序结构，这是冻结在自旋玻璃状状态在低温下，在表面的铁氧化物壳微晶或整个较薄的铁氧化物壳层。
We systematically studied electrical resistivity and magnetoresistance (MR) of size-monodispersed oxide-coated Fe cluster assemblies with the mean cluster sizes of d = 9–17 nm prepared by a plasma-gas-condensation-type cluster beam deposition system. The electrical resistivity and magnetoresistance strongly depend on the temperature, surface oxidization degree of the clusters (namely O2 gas flow ratio RO2), Fe cluster size d, and magnetic field. The oxide-coated Fe cluster assemblies exhibit a large negative MR effect which is further enhanced at low temperatures due to the dominant contribution of the spin-dependent tunneling process between the Fe cores through the oxide shell layers. It has been found that the magnetic field dependence of the MR ratio at all temperatures shows no saturation tendency up to a maximum field H = 50 kOe and completely disagrees with the magnetization curves which indicate a saturation tendency. These results have been interpreted by consideration of the magnetic state of the Fe-oxide shell layers, spin-dependent tunneling mechanism, and intercluster magnetic correlation. The high-field nonsaturation behavior in the magnetoresistance effect is attributed to the spin-disordered structure, which is frozen in a spin-glass-like state at low temperatures, in the surface of the Fe-oxide shell crystallites or the whole thinner Fe-oxide shell layers.