Effect of Milling on the Intrinsic Coercivity of Barium Ferrite Powders

The effect of milling on the intrinsic coercive force of Ba ferrite powders has been ascribed to (1) thermal fluctuations caused by superparamagnetic fine particles and (2) lattice defects introduced by milling. To test these interpretations, the Moessbauer absorption spectra and angular variation of coercive force for ball-milled powders were determined. With increasing milling time, the Moessbauer absorption spectrum becomes ambiguous, and the absorption lines are broadened; the quadrupole-split center line corresponding to superparamagnetic BaFe₁₂O₁₉ cannot be detected. The angular variation of coercive force shows that milling considerably lowers either the nucleation field of the reverse domain or the effective anisotropy field or both. It is concluded that lattice defects, rather than superparamagnetic fine particles introduced by milling, greatly affect the intrinsic coercive force of Ba ferrite powders.