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。主要研究结果如下：(1)在用电子光刻技术制备的NiFe铁磁纳米环中，由于Aharonov玻姆效应，出现了明显的磁阻振荡。(2)在Ni量子线中发现了外加磁场和电场对电导量子化的影响。所有结果表明，尽管传导电子可能由于局域自旋而发生强散射，但传导电子的相干性决定了纳米铁磁体的输运性质。此外，观测到的量子化电导的外场依赖关系表明，磁结构在铁磁体中电子的弹道输运中扮演着重要的角色。另一方面，到目前为止，还没有观察到铁磁体的磁结构和扩散输运之间的关联，这是理论上预测的。利用纳米磁铁研究这种关联的一些实验正在进行中，其中的磁结构可以通过磁形各向异性和外加磁场来控制。

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.