SCANNING ELECTRON-MICROSCOPY WITH POLARIZATION ANALYSIS (SEMPA)

The high spatial resolution imaging of magnetic microstructure has important ramifications for both fundamental studies of magnetism and the technology surrounding the magnetic recording industry. One technique for imaging surface magnetic microstructure on the 10-nm-length scale is scanning electron microscopy with polarization analysis (SEMPA). This technique employs a scanning electron microscope (SEM) electron optical column to form a medium energy (10-50 keV), small probe (<50 nm) of high current (>1 nA) on a ferromagnetic specimen. Secondary electrons excited in the ferromagnet by the high spatial resolution probe retain their spin-polarization orientation as they leave the sample surface. The spin polarization of the emitted secondary electrons can be related directly to the local magnetization orientation. A surface magnetization map is generated when the spin polarization of the secondary electrons is analyzed as the electron beam is rastered point-by-point across the ferromagnet's surface. In this review article we review the important instrumental components characterizing the SEMPA system. Characteristics of the electron probe forming optics, electron spin-polarization analyzers with associated transport optics, and signal processing electronics will be described. Emphasis on the fundamental design requirements will be stressed. Data acquisition, storage, and processing, as it applies specifically to SEMPA, will be reviewed. Instrumental artifacts specific to SEMPA will be outlined and techniques for their correction given. Examples of magnetic images at high spatial resolution will be shown.