  We demonstrate control of magnetic domain structures in continuous FePd thin
films by patterning their surfaces with plasma treatment. The Fe-oxide layer
formed on the surface upon ambient exposure of the FePd alloy thin film grown
on an Al$_2$O$_3$(0001) substrate was patterned into microstructures by e-beam
lithography followed by O$_2$- or Ar-plasma treatment. Microscopic pinning of
magnetic domain walls in the thin films is then observed by magneto-optic Kerr
effect microscopy, with the magnetic field needed to reverse the magnetization
of the plasma-treated areas being larger than that for the untreated areas. An
intriguing competition between the uniaxial anisotropy and the exchange bias is
also observed in the system. This study demonstrates that patterning of the
film surface with plasma treatment can be an easy and efficient method for
sophisticated engineering of magnetic structures in thin films, and therefore
has potential application in developing future data-storage and spintronic
devices.
