Scanning electron microscopy with polarization analysis studies of Ni-Fe magnetic memory elements

The authors describe the use of scanning electron microscopy with polarization analysis (SEMPA) to image the magnetic structure of Permalloy magnetic memory elements quantitatively. Various methods of determining the absolute magnitude and direction of the magnetization vector are described. The magnetic domain structures are observed as a function of ion milling time. During ion milling the surface composition is monitored by Auger analysis. Experimental results are presented for Permalloy memory elements. Two methods of determining and eliminating spurious apparatus asymmetries in SEMPA measurements were used. The first relied on assumptions about the symmetry of the domain pattern to establish the polarization zero. In general, this produced accurate maps of the magnetization direction as long as false asymmetries due to surface topography were not important. The second method used the spin-independent scattering from a graphite target as a reference. This method eliminated the instrumental and topographic asymmetry and is preferred for absolute, quantitative magnetization measurements. Both methods permit the angle of the magnetization vector to be measured to within ±10°