Magnetic viscosity in the magnetic fine powders

Givord et al. found that the activation volume is proportional to the cube of the domain wall width for Sr-ferrite. Carmona et al. suggested that the viscosity mechanism in Ba-ferrite is the strong pinning of domain walls. In this paper, we investigate the temperature dependence and size dependence of the magnetic viscosity of Ba-ferrite and γ-Fe
₂
O
₃
fine powders in order to reveal the coersivity mechanism in these materials.