Magnetic granular films, which consist of magnetic fine particles of nanometer size and a nonmagnetic matrix, have been of great interest for new magnetic materials. Their magnetic characteristics strongly depend on the fine structures, besides the combination of magnetic and nonmagnetic constituents, especially their surface topology and the particles size. Although the relationship between these fine topological structures and the macro-magnetic characteristics has been investigated systematically by many researchers, there has remained a desire to observe magnetic microstructures directly. We succeeded in observing the magnetic structure of fine particles in granular films using Lorentz microscopy.

Two kinds of specimens were observed. One was an Fe-Mo granular film. An amorphous film of Fe-Mo was prepared by dc magnetron sputtering on amorphous carbon thin films at a temperature below 180 K. The films were annealed at 770 K within an in-plane magnetic field. The other kind was an Fe-MgO granular film, where iron particles were embedded in a magnesium oxide single crystal.