Spin-Topology and Quantum Magnetics in Nano-Structured Magnetic Materials

本文研究了纳米结构磁体的自旋拓扑和量子磁学。本文的研究结果总结如下：1)利用一种新的畴壁共振谱法，确定了半圆形纳米线中磁壁的质量为6.6 × 10-23 kg，与1948年多林（V. W. Doring）的预测结果吻合得很好。结果表明，畴壁是由低交流电流密度驱动的，可以忽略小焦耳加热。2)利用MFM和磁电阻研究了坡莫合金丝蜂窝网络的磁性结构和磁化过程。发现磁结构受磁相互作用支配，与冰律相似。通过降低网络顶点的交换能量，冰规则型相互作用引起磁化过程的转变。3)测量了三层Py/Cu/Py纳米环的磁阻。该环检测由非均匀磁化分布调制的电子相干性。4)研究了电导量子化时弹道纳米触点的磁阻效应和电流-电压特性。触点中的自旋排列对量子电导起着重要的作用。5)利用Py薄膜的铁磁共振，在室温下观察了Py/Pt薄膜中自旋霍尔效应的逆过程。6)研究了单根铁磁纳米线在射频范围内的导通，阐明了自旋转矩二极管效应与磁场和频率的关系。

This study is on the spin-topology and quantum magnetics in nano-structured magnets. The results of the present study are summarized as follows ;1)By using a new domain wall resonance spectroscopy, the mass of a magnetic wall in a semi-circle nano-line is determined to be 6.6x10-23 kg, the value of which is well in agreement with that predicted by V. W. Doring in 1948. It is shown that the domain wall is driven by low AC current density which enables negligible small Joule heating.2)The magnetic structure and magnetization process in a Permalloy wire-based honeycomb network have been investigated by means of MFM and magnetoresistance. It is found that the magnetic structure is governed by magnetic interaction similar to the ice rule. By decreasing the exchange energy at the vertices of the network, the ice-rule type of interaction causes a transition of the magnetization process.3)Magnetoresistance for tri-layered Py/Cu/Py nanoring is measured. The ring detects the electron coherence modulated by the inhomogeneous magnetization distribution.4)The magnetoresistance effect and the current-voltage characteristics in ballistic nano-contacts in the regime of conductance quantization are investigated. The spin arrangement in the contacts plays an important role for quantum conductance.5)The inverse process of the spin-Hall effect is observed at room temperature in a Py/Pt thin film by the ferromagnetic resonance of Py film.6)The conduction of a single ferromagnetic nanowire in a radio frequency range is investigated and the magnetic field and frequency dependences of the spin torque diode effect are clarified.