Magnetic domain observations in Fe-Ga alloys

The domain structure of Fe-Ga bulk alloys is investigated with magnetic force (MFM) and magneto-optic Kerr microscopy. Published domain observations on this class of materials predominantly reveal maze-like domain patterns that indicate out-of-plane magnetization, i.e. out-of-plane anisotropy. Contrary to the belief that this anisotropy is due to the presence of nanoscale heterogeneities (Bai et al., 2005, 2009), we show that it is due to a damaged surface layer caused by standard mechanical polishing. The surface conditions in Fe-Ga alloys are more sensitive to stress-induced damage than in pure α-Fe. This is explained as being due to increased magnetostriction. We demonstrate that the damaged surface layer can be removed with an additional polishing step using colloidal amorphous silica. On (0 0 1) bulk crystal surfaces, the domain structures, obtained after the removal of the damaged surface layer, reveal in-plane magnetization with sharp and straight 90 deg. and 180 deg. domain walls that are expected in these alloys.