SPIN-POLARISED TUNNELING EFFECTS OBSERVED ON THE MAGNETITE (001) AND (111) SURFACES

摘要

The (001) and (111) surface structure of magnetite have been studied using Auger electron spectroscopy, low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). A clean surface was obtained by a combination of in-situ annealing in oxygen atmosphere, Argon sputtering and subsequent annealing in UHV for Fe_3O_4 (001) and (111) surfaces. A (2~(1/2) x 2~(1/2))R45° superlattice was found by LEED and STM on the Fe_3O_4 (001) surface. Evidence of the formation of a superstructure on the surface of Fe_3O_4 (111) single crystal is given. The superstructure, which has a periodicity of 42 A and the three-fold symmetry, has been observed by means of STM and LEED. Atomic resolution STM images have been achieved on the Fe_3O_4 (001) and (111) surface using MnNi tips, which are interpreted in terms of spin-polarized effect.