Magnetic force microscopy study of new nanocrystalline soft magnetic ribbons.

New nanocrystalline, multicomponent extremely soft magnetic materials with superior high temperature magnetic properties hold great promise in power applications. Fabricated in ribbon form by rapid solidification methods, the initial material is amorphous. By controlled annealing procedures, the amorphous material was transformed into a nanocrystalline form with the degree of crystallinity determined by the annealing temperature and time. The magnetic structures of ribbons, as-fabricated and annealed at temperatures from 550 to 750 degrees C were examined by magnetic force microscopy to determine the impact of residual stress and nanocrystallinity on the observed structure. A correlation was seen between the magnetic structures and surface microstructure. The wheel side of the as-processed ribbon was rougher than the top side of the ribbon and a complicated magnetic domain structure was present in the amorphous material. After annealing, nanocrystals formed, increasing in size with increasing temperature. The lowest temperature annealed sample had a bimodal grain size distribution and a combination of stripe and localized domains. After annealing little difference was seen between the two sides of the ribbons. Stripe domains were absent in the ribbons annealed at the highest temperatures.