Effect of dichroism in the GaAs-tip-based spin polarized STM

In this paper, we investigate the origin of spurious signals in the GaAs-ti p-based spin-polarized scanning tunneling microscope setup. Experimentally as well as theoretically, dichroism and birefringence are found to induce a power modulation signal up to a 10% depth. In particular, the presence of dichroism fluctuations in the sample's substrate, at a submicronic scale an d of non-magnetic origin, led to the formation of an image showing a domain -like structure on a mica/Au (10 nm) non-magnetic sample. As a conclusion, this parasitic signal is therefore competing with the expected spin-depende nt tunneling conductance phenomenon. Finally, we discuss of a new image obt ained with a high-quality, microfabricated tips, where both phenomena may b e present at the same time. (C) 1999 Elsevier Science B.V. All rights reser ved.