Spin-polarized scanning tunneling microscopy and spectroscopy of ferromagnetic Dy(0001)/W(110) films

摘要

Spin-polarized scanning tunneling microscopy and spectroscopy (SP-STS) are employed to investigate the contrast mechanism and the magnetic structure of Dy films epitaxially grown on W(110). While relatively complicated tip preparation procedures were necessary in the past, we now obtain magnetic contrast by bringing the tip in gentle contact with a ferromagnetic Dy film. Maximum contrast is observed at bias voltages around -0.9 V. Since highly polarized sample states are not available at the corresponding binding energy, we suggest that an unoccupied tip state is responsible for the strong magnetic contrast. SP-STS measurements show three-, four-, or sixfold magnetic contrast. This result can be explained by random azimuthal orientations of the tip magnetization with respect to the sample's easy axis. Images of the magnetic domain structure show a stripe domain pattern which consists of about 40 nm wide domains, the magnetization directions of which alternate by 60°. This result is a clear proof that the Dy(0001) surface exhibits ferromagnetic order. The domain walls are identified as Neel walls with a width of 2-5 nm.