On the nature of defects in barium ferrite platelets

Barium ferrite (Ba.0.6Fe2O3) platelets of approximately m diameter and with intrinsic coercive force of about 5000 Oe were crystallized from a glass phase. To study the nature of the defects and their influence on the magnetic properties, the crystailized glass was plastically deformed by applying a pressure of 30 kbar in an opposed anvil press. Barium ferrite platelets were extracted from the crystailized glass by leaching the matrix in acetic acid. Magnetic measurements indicated 1 to 2 percent increase in saturation magnetization and about 40 percent decrease in coercive force in the deformed platelets compared to the properties in the undeformed platelets. Transmission electron microscopy revealed deformation twins, nonbasal slip, and stacking faults in the deformed platelets. In another experiment, the platelets after leaching the matrix were deformed at 30-kbar pressure. Saturation magnetization decreased by 9 percent and coercive force by 55 percent. The results are discussed by comparing with the changes in properties obtained in ball milled powders. Annealing the deformed powders resulted in partial recovery of saturation magnetization and coercive force to the original undeformed state.