Magneto-optical interference effect in metalic thin films with nano-structures

本研究的目的是建立一种新的磁光衍射技术来评价亚微米级铁磁性物质的磁性状态，并研究磁性状态与电子输运性质之间的关系。为此，利用新研制的磁光衍射仪、SQUID磁强计、高精度电阻率测量设备和磁力显微镜，对二维亚微米尺度的点阵和线阵进行了系统的研究。在磁光方面，由于阵列结构的不同，衍射光的级数不同，可以适应显著的磁光克尔效应。通过考虑周期磁结构和阵列结构的傅里叶变换，成功地计算了局部磁畴结构。此外，还发现锥形衍射几何中的衍射光表现出克尔效应，这为在没有分析器的情况下获得导线中的磁信息提供了一种可能的方法。输运实验首次证明，单个磁区壁可以被捕获在亚微米宽的导线或成对的圆点中。发现电阻率的明显变化与磁畴壁的成核和湮没有关。这一新现象不能用传统的各向异性磁阻来解释。认为抑制弱局域化是一种可能的机制。对Fe和Co外延线进行了相同类型的系统研究，结果表明，周期域壁在外延线中是稳定的。在这种情况下，周期磁区壁对内场的调制是导致电阻率降低的原因，也就是表面散射的减小。

The purpose of this study is to establish a novel magneto-optical diffraction technique to evaluate magnetic state in a sub-micron scale ferromagnetic substance, and to study the correlation between the magnetic state and the electronic transport properties. For this purpose, systematic studies on the 2 dimensional submicron scale dot and wire arrays were carried out by using a newly constructed magneto-optical diffractometer, a SQUID magnetometer, a high precision resistivity measurement equipment, and a magnetic force microscope. As for magneto-optics, the different orders of the diffracted light due to the array structure was found to accomodate significant magneto-optical Kerr effects. The local magnetic domain structure was successfully evaluated by taking into account the Fourier transforms of the periodical magnetic and array structures. Furthermore the diffracted light in a conical diffraction geometry was found to show Kerr effect, which provided a possible method to obtain magnetic information in the wire without an analyser. The transport experiments for the first time demonstrated that a single domain wall can be trapped in either the submicron wide wire or paired circular dots. A clear change in resistivity was found to appear in association with the domain wall nucleation and annihilation. This new phenomenon can not be explained by considering the conventional anisotropy magnetoresistance. The suppression of weak localization is suggested to be a possible mechanism. The same type of systematical studies were performed on the epitaxial Fe and Co wires, demonstrating that periodical domain walls can be stabilized in the wire. In this case, the modulation of the internal field due to the periodical domain walls are found responsible for the reduction in resistivity, that is the reduction of the surface scattering.