High-Resolution Studies of Magnetic Domains in MnBi Films

Magnetic domains existing during the magnetization reversal in oriented low-temperature phase MnBi films have been observed at room temperature by decorating the domains with iron particles obtained and brought onto the film investigated by evaporating iron in an argon atmosphere onto the film. By making a carbon replica of the film surface, the domains can be observed electron microscopically. The resolution obtained is 0.05 μm. The domain width in a 100-nm-thick MnBi film without applied field is approximately 0.35 μm. It increases with decreasing film thickness. Before the films reach saturation, bubble domains with diameters smaller than 0.5 μm are observed. Along minor hysteresis loops, filament domain configurations are observed. The width of the filament domains decreases with increasing strength of a field applied perpendicular to the film plane. The width is approximately 0.1 μm in a 90-nm-thick MnBi film with an applied field of 344 kA/m. The wall-energy density in MnBi film is estimated to be 2×10−3 W sec/m2.