Influence of stress on the high coercive force of gamma -Fe2O3 thin films

Nontextured gamma -Fe₂O₃ polycrystalline films have been obtained by oxidation of magnetic films deposited by a modified OMCVD (organometallic chemical vapor deposition) technique. The influence of the stress on the crystallographic and magnetic properties of the films has been studied in regard to the experimental deposition conditions. The sin² Psi method has been used to determine the origin of these stresses. Two kinds of stresses affect the iron oxide films: thermal stress and oxidation stress. The completely oxidized gamma -Fe₂O₃ films are shown to be in a tensile planar state that leads to an induced perpendicular anisotropy through magnetostrictive coupling. Controlling the experimental parameters (substrate temperature, annealing conditions, grain size) makes it possible to obtain perpendicular coercive force values of about 90 Oe. This high coercive force is associated with a stress of 10¹⁰ dyne/cm², which does not seem to affect the film adherence.