Mechanism of Quantum Transportation and Macroscopic Quantum Tunnel Effect in Nanomagnets

研究了纳米磁体中的扩散电子输运和弹道电子输运。结果表明：（1）在电子光刻制备的铁磁NiFe纳米环中，由于Aharonov-Bohm效应，磁电阻出现了明显的振荡。(2)在Ni量子线中发现了电导量子化的外磁场和电场依赖性。所有的结果表明，在纳米级铁磁体中的传导电子的相干性主导的输运性质，尽管可能的强散射的传导电子由于本地自旋。此外，所观察到的量子化电导的外场依赖性意味着在铁磁体中的电子的弹道输运的磁结构的重要作用。另一方面，磁结构和扩散输运之间的相关性，这已经在铁磁体的理论预测，尚未观察到迄今为止在本研究中。现在正在考虑使用纳米磁体进行相关性研究的一些实验，其中可以根据磁形状各向异性和额外磁场来控制磁结构。

Diffusive as well as ballistic electronic transportation in nanomagnets has been investigated. The results are summed up as follows: (1) A conspicuous oscillation of magnetoresistance due to the Aharonov Bohm effect was found in a ferromagnetic NiFe nano-ring fabricated using the electron lithography. (2) The external magnetic and electric field dependence of the conductance quantization was found in Ni quantum wires. All the results indicate that the coherence of a conduction electron dominates the transport property in nanoscale ferromagnets in spite of the possible strong scattering of the conduction electron due to the local spins. Furthermore, the observed external-field dependence of the quantized conductance implies an important role of the magnetic structure in the ballistic transportation of electron in ferromagnets. On the other hand, correlations between the magnetic structures and the diffusive transportation, which has been theoretically predicted in ferromagnets, have not been observed so far in the present study. Some experiments for the investigation of the correlation using nanomagnets in which the magnetic structures can be controlled in terms of the magnetic shape anisotropy and the extra magnetic field are now under contemplation.