Magnetic domain wall contrast under zero domain contrast conditions in spin polarized low energy electron microscopy

Highlights: • Magnetic contrast changes sign because of the energy-dependence of the spin reflectivity asymmetry. • Unexpected magnetic contrast is observed at magnetic domain boundary at the energy of zero asymmetry. • This contrast results from the finite energy width of the electron source, in combination with the dispersion of the magnetic prism array. -- Abstract: Important applications of spin polarized low energy electron microscopy (SPLEEM) employ this technique's vector imaging capability to resolve domain wall (DW) spin textures. Studying several thin film systems including Co/W(110), Co/Cu(001) and (Co/Ni)_n/W(110), we show that an additional contrast can appear at magnetic DWs. By imaging the magnetization as a function of electron landing energy, electron energies are selected at which the magnetic domain contrast vanishes. Surprisingly, under such conditions of zero contrast between magnetic domains, we observe the appearance of magnetic contrast outlining the DWs. This DW contrast does not depend on the DW spin texture. Instead, our measurements show that this DW contrast results from a combination of the energy-dependence of the spin reflectivity asymmetry of the magnetic film, the finite energy width of the spin polarized electron source, and the dispersion of the magnetic prism array that separates the illumination and imaging columns of the instrument. Awareness of this DW contrast mechanism is useful to aid correct interpretation of SPLEEM images.