Secondary electrons from a ferromagnet exhibit a spin polarization related to the net spin density of the valence electrons, i.e., directly proportional to the magnetization. Thus, secondary electron polarization analysis provides a direct measurement of the magnitude and direction of the magnetization in the area probed by the incident electron beam in the Scanning Electron Microscope (SEM). The polarization measurement is independent of topographic contrast and is obtained simultaneously with the conventional topographic image. A new , compact (approximately fist-sized), polarization analyzer utilizing low energy (150 eV) diffuse scattering from a polucrystalline Au target was specially developed for this application. The small sizw of the spin analyzer allowed the use of two orthogonal analyzers on a field emission SEM to detect all three components of the magnetization vector. Images from Fe-3%Si demonstrate the independence of magnetic and topographical contrast except in special cases where the topography affects the magnetism, e.g., by pinning domain walls. Practical application of Scanning Electron Microscopy with Polarization Analysis (SEMPA) to study closure domains in permalloy thin film recording heads and to observe the magnetic microstructure of CoNi thin film recording high density media will be discussed. The variation of the spin within a domain wall of an Fe-based ferromagnetic glass is observed.
Citation: Scanning Microscopy
Pub Type: Journals