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等磁性多层膜的巨磁电阻效应中起着重要的作用。界面的粗糙度，即界面上的原子无序，预计会伴随着磁无序。这种磁无序可能直接影响GMR效应，因为传导电子在界面上的自旋相关散射被认为是GMR效应的关键。然而，在研究巨磁电阻效应时，对界面磁无序的关注很少。此外，界面粗糙度这一术语的含义似乎并不明确。在本研究中，我们将界面圆度定义为自仿射的分形界面度，并试图建立磁性界面粗糙度的定量分析。为了提高入射偏振中子的强度，在高能加速器组织的偏振中子反射仪孔道上安装了由Fe/Si超反射镜组成的聚焦偏振中子装置。利用这种新装置，我们成功地增加了两倍以上的中子数。通过中子和X射线反射率的测量，研究了外延Fe/Cr(001)多层膜界面粗糙度与巨磁电阻效应之间的关系。样品在不同的真空条件下进行热处理，以获得不同的界面粗糙度。采用自仿射-分形界面法对镜外反射的细节轮廓进行了定量分析。磁性界面粗糙度对退火工艺非常敏感，而原子界面粗糙度对退火工艺的敏感性较低。这表明，对于界面处与自旋无关的电子散射，磁性界面粗糙度优于原子界面粗糙度，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.