Strongly coercive films of &ggr;Fe2O3‐Fe3O4solid solution [xFe8/3O4‐(1−x)Fe3O4] have been deposited using a new pyrolysis technique. The magnetic and crystallographic properties of nonoxidized Fe3O4(x=0) and completely oxidized &ggr;Fe2O3(x=1) films are shown to be closely related to the planar stress present in the films. An x‐ray method is proposed for the study of the iron oxide film stress. The different results are applied to understand the origin of the strong coercive force of partially oxidized solid solution films.