Coercivity reduction in thin orthoferrite plates by annealing

High temperature annealing of thin polished plates of rare-earth orthoferrites has been found highly effective in reducing the coercivity resulting from mechanical processing. The annealing atmosphere must be oxygen or an oxygen-inert gas mixture free of reactive contaminants such as water vapor, carbon dioxide, and platinum oxide. Chemical reactions through contact of orthoferrite with other materials must be avoided. Annealing below 1000°C relieves elastic and plastic surface strains and is characterized by an activation energy of 5.8 × 10³cal/mole or 0.25 eV/molecule. Temperatures near 1500°C are required to remove brittle fracture damage. High temperature annealing may also be effective in reducing the coercivity caused by some bulk defects. The annealing process is capable of producing high quality orthoferrite plates suitable for domain propagation devices.