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 [1,2] (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 (001) bulk crystal surfaces, the domain structures, obtained after the removal of the damaged surface layer, reveal in-plane magnetization with sharp and straight 90° and 180° domain walls that are expected in these alloys.