Spin injection into magnetic alloys using optical spin excitation technique

利用磁控溅射和反应分子束外延技术，研究了在铁磁金属/GaAs界面上，利用磁控溅射和反应分子束外延技术生长了Fe/GaAs、Fe/MgO/GaAs、Fe3O4/GaAs等几种样品，研究了在铁磁金属/GaAs界面上激发的自旋极化电子的自旋过滤效应。用波长为800~850 nm的右或左圆偏振光从样品的法线方向穿过磁层，在垂直于薄膜平面的磁场中检测到螺旋度相关的光电流。螺旋度依赖的光电流表现出明显的场依赖关系，与磁层的磁化过程相对应。在足以饱和磁化的磁场中，还测量了螺旋度相关的光电流的偏置依赖关系。磁圆二向色性在Fe/GaAs样品的反向偏置中占主导地位，而在正向偏置时观察到显著的特征。我们将这一特征归因于Fe/GaAs界面上的自旋过滤效应对螺旋度相关光电流的偏置依赖。然而，自旋过滤的效率被限制在几个%的范围内。此外，在界面处插入氧化镁隧道势垒并不能显著提高效率，这可能是由于氧化镁层的粗糙度和针孔的存在。对于Fe_3O_4/GaAs样品，我们在零偏压下观察到了与螺旋度相关的光电流的偏置特性.综合这些结果，我们得出结论：磁性金属层可以起到自旋滤光器和自旋探测器的作用，尽管效率很低.原子平坦层是提高自旋探测效率所必需的。

The purpose of this study is to examine the spin filtering effect of spin polarized electrons excited in GaAs with illumination of circularly polarized light at the ferromagnetic metal/GaAs interfaces.Several types of samples, e.g., Fe/GaAs, Fe/MgO/GaAs, Fe_3O_4/GaAs, were grown using magnetron sputtering and reactive MBE techniques. These samples were illuminated with right or left circularly polarized light with a wavelength of 800-850 nm from sample normal direction through the magnetic layer, thereby helicity dependent photocurrent was detected in a magnetic field normal to the film plane. The helicity dependent photocurrent showed clear field dependence, corresponding to the magnetization process of the magnetic layer. The bias dependence of the helicity dependent photocurrent was also measured in a magnetic field sufficient to saturate the magnetization. Magnetic circular dichroism was predominant for reverse bias for Fe/GaAs samples, while a significant feature was observed at a forward bias. We attribute this characteristic feature in the bias dependence of helicity dependent photocurrent to spin filtering effect at the Fe/GaAs interface. The efficiency of the spin filtering, however, is limited to a value to a few %. Also, any significant enhancement in the efficiency was not obtained by inserting an MgO tunneling barrier at the interface, presumably due to the roughness of the Mg0 layer and the presence of pin holes. For Fe_3O_4/GaAs samples, we observed a similar feature in the bias dependence of the helicity dependent photocurret at zero bias.From these combined results, we conclude that magnetic metal layer can act as a spin filter and work as a spin detector, although the efficiency is small. Atomically flat layers are necessary to improve the spin detection efficiency.