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Magnetic imaging with scanning probe microscopy

机译：用扫描探针显微镜进行磁成像

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We review our research on the application of scanning tunnelling microscopy (STM) and non-contact atomic force microscopy (NC-AFM) for magnetic imaging in high spatial resolution even down to the atomic scale. In the first part, we propose a new experimental scheme of spin-polarized STM (SP-STM) with a GaAs spin probe to obtain a large contribution of spin-polarized electrons in the tunnelling current. This is yielded by injecting the spin-polarized photo-excited electrons in an optically pumped GaAs tip into the spin-polarized empty states near the Fermi level of a bcc-Fe(001) surface. According to the bandgap energy of GaAs and the surface state of the sample observed at 0.4 eV above the Fermi level, the spin-dependant electron injection can be achieved by applying a sample bias voltage of -1 V. The tunnel current in the positive bias region depends on the helicity of the circular polarized pumping light, and is modified when the applied magnetic field is reversed. Mapping the current asymmetry provides a spin-dependent SP-STM image. In the second part, we describe the progress towards spin imaging with NC-AFM. The spin imaging can be achieved by detecting short-range magnetic interaction such as exchange interaction between a ferromagnetic tip and a magnetic sample. We demonstrate the capabilities of NC-AFM by imaging the spin structure of an antiferromagnetic NiO(001) surface on the atomic scale. The cross-sectional line profiles of the atomically resolved images obtained using several ferromagnetic tips (Fe, Ni) were analysed by adding the atomic corrugation amplitude on the basis of the periodicity of the image. The results of the analysis show that the difference of the neighbouring maxima depends on the crystal direction. On the other hand, no significant indication of the directional dependency can be seen on the images obtained by using a non-magnetic Si tip. The directional dependency coincides with the antiferromagnetic spin alignment of the NiO(001) surface.
机译：我们回顾了我们在扫描隧道显微镜（STM）和非接触式原子力显微镜（NC-AFM）的应用中对高空间分辨率甚至低至原子尺度的磁成像应用的研究。在第一部分中，我们提出了一种具有GaAs自旋探针的自旋极化STM（SP-STM）的新实验方案，以在隧道电流中获得自旋极化电子的巨大贡献。这是通过将光学泵浦的GaAs尖端中的自旋极化的光激发电子注入到bcc-Fe（001）表面费米能级附近的自旋极化的空态中来实现的。根据GaAs的带隙能量和在费米能级以上0.4 eV处观察到的样品表面状态，可以通过施加-1 V的样品偏置电压来实现自旋依赖性电子注入。正偏置中的隧道电流区域取决于圆偏振泵浦光的螺旋度，并且当施加的磁场反转时会改变。映射当前不对称性可提供自旋相关的SP-STM图像。在第二部分中，我们描述了使用NC-AFM进行自旋成像的进展。自旋成像可以通过检测短距离磁相互作用（例如铁磁尖端和磁性样品之间的交换相互作用）来实现。我们通过在原子尺度上成像反铁磁NiO（001）表面的自旋结构来证明NC-AFM的功能。通过基于图像周期性添加原子波纹幅度，分析了使用多个铁磁尖端（Fe，Ni）获得的原子分辨图像的截面轮廓。分析结果表明，相邻最大值的差取决于晶体方向。另一方面，在通过使用非磁性Si尖端获得的图像上看不到方向依赖性的显着指示。方向依赖性与NiO（001）表面的反铁磁自旋对准一致。

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