Microscopic magnetization reversal processes and magnetic domain structure in epitaxial Fe/GaAs(001) films

Abstract

We report the results of Lorentz electron microscopy studies of the microscopic magnetic reversal behavior of epitaxial Fe/GaAs(001) thin films in the thickness range 150--450 \AA{} in order to explain how the microscopic processes give rise to the observed macroscopic reversal behavior. The results are described in the context of scanning tunneling microscopy and transmission electron microscopy studies of the film microstructure and of magneto-optical Kerr effect magnetometry studies of the macroscopic magnetic switching behavior. We find that striking differences in the domain structure occur according to the crystallographic direction along which the field is applied. For applied fields aligned close to the in-plane 〈110〉 directions (hard axes), magnetization reversal proceeds via a combination of coherent rotation and displacements of 90\ifmmode^\circ\else\textdegree\fi{} domain walls aligned along the 〈110〉 directions. For magnetization reversal along the in-plane 〈100〉 directions (easy axes), an irregular checkerboard domain structure develops at the transition field: well-defined 90\ifmmode^\circ\else\textdegree\fi{} and 180\ifmmode^\circ\else\textdegree\fi{} domain walls coexist, aligned along the 〈110〉 and 〈100〉 directions, respectively. The magnetization reversal along the 〈100〉 directions takes place via a combination of domain nucleation and wall displacements. The magnetic reversal of unfavorably oriented domains is found to occur by a combination of two 90\ifmmode^\circ\else\textdegree\fi{} reorientations.