A current scientific challenge with many ramifications for magnetic technology is to image magnetic microstructure with the highest possible spatial resolution in order to observe magnetic domains or even spin configurations within a domain wall. Ultimately one can envision imaging the magnetic moment of individual atoms which would also make possible the observation of antiferromagnetic structures. The measurement of the spin polarization of secondary electrons generated by a finely focused (unpolarized) scanning electron microscope (SEM) beam to obtain high-resolution magnetization images is present. An alternative measurement, using a spin-polarized incident beam in an SEM, has many difficulties which are discussed. To measure spin configurations with higher spatial resolution, the possibility of introducing electron spin polarization in scanning field-emission and tunneling microscopy is considered. The measurement of the spin polarization of secondary electrons generated by a specially prepared single-atom scanning field-emission tip looks promising. High-resolution imaging of spin configurations in scanning tunneling microscopy appears possible if the tip itself is a source of spin-polarized electrons. The potential advantages and unsolved problems involved in using a ferromagnetic tip or an optically pumped semiconductor tip are described.
Citation: Physica Scripta
Pub Type: Journals