Surface and internal magnetic domain structures of Fe-Ga alloy rods

The magnetic domain structures of the < 100 > oriented Fe81Ga19 polycrystalline alloys with rapid quenching (RQ) and post-annealing (PA) thermal treatments are investigated by using magnetic force microscopy (MFM). The surfaces of the RQ alloy rods take on the dendritic domains after undergoing a standard mechanical polishing. While after PA processing, the distinct domain structures are observed at different temperatures. The wide stripe-like domain patterns appear in the surface of those PA rods at 550 degrees C while the ramous domains remain at 400 degrees C annealing. X-ray diffraction patterns indicate that a thin iron layer is formed on the surface of the specimens annealed at higher temperature. The soft magnetic iron layer, actually acting as a shield for the stray fields emerging from the internal magnetic structures underneath, brings about the presentation of the wide internal domains.