Controll and Quantitative Analysis of Spin Disorder at Magnetic fractal Interface

众所周知，界面粗糙度在Fe/Cr、Co/Cu等磁性多层材料的巨磁阻效应中起着重要的作用。界面粗糙度，即界面上的原子无序，预计会伴随着磁性无序。由于导电电子在界面处的自旋相关散射被认为是GMR效应所必需的，因此这种磁性无序性可能直接影响GMR效应。然而，在GMR效应的研究中，很少关注界面处的磁性紊乱。此外，“界面粗糙度”一词的含义似乎也没有明确定义。本研究将界面粗糙度定义为自仿射分形界面所描述的界面粗糙度，并尝试建立磁性界面粗糙度的定量分析方法。为了提高入射极化中子的强度，在高能加速器机构的极化中子反射计PORE上安装了由铁硅超镜组成的聚焦极化中子装置。我们用这种新装置成功地使中子数增加了一倍以上。利用中子反射率和x射线反射率测量研究了Fe/Cr（001）外延多层膜中界面粗糙度与GMR效应的关系。在真空中对试样进行了不同条件下的退火处理，使试样具有不同的界面粗糙度。采用自仿射分形界面模型定量分析了非镜面反射的详细剖面。磁性界面粗糙度对退火过程非常敏感，而原子界面粗糙度对退火过程不太敏感。这表明磁界面韧性比原子界面粗糙度对界面上的自旋无关电子散射起主导作用，这对GMR效应是不利的。

It is well known that the interfacial roughness plays an important role in the giant magnetoresistance (GMR) effect of magnetic multilayers like Fe/Cr, Co/Cu and so on. The interfacial roughness, atomic disorder at the interfaces, is expected to be accompanied with the magnetic disorder. Such magnetic disorder may directly affect on the GMR effect because the spin-dependent scattering of conduction electrons at the interface is believed to be essential to the GMR effect. However, little attention has been paid to the magnetic disorder at the interface in studying the GMR effect. In addition, the meaning of the term, interfacial roughness, seems not to be well-defined. In this study we defined the interfacial rouness as that described by self-affine the Fractal interface and made an effort to establish the quantitative analysis of the magnetic interfacial roughness.A focusing polarizing neutron device which consists of Fe/Si supermirrors was installed at a polarized neutron reflectometer, PORE, at High Energy Accelerator Organization in order to increase the intensity of incident polarized neutrons. We have successfully increased the neutrons more than twice using the new device.The correlation between interfacial roughness and the GMR effect in epitaxial Fe/Cr(001) multilayers was investigated by neutron and X-ray reflectivity measurements. The specimens were annealed under various conditions in vacuum so as to have different interfacial roughnesses. The detailed profile of the off-specula reflection was quantitatively analyzed by the self-affine-Fractal interface model. The magnetic interfacial roughness were very sensitive to the annealing process, on the other hand, those for the atomic interfacial roughness were less sensitive. This suggests that the magnetic interfacial foughness in dominant over the atomic interfacial roughness for the spin-independent electron scattering at the interface which is a disadvantage to the GMR effect.