Hopkinson Effect Study in Spinel and Hexagonal Ferrites

The magnetic susceptibility shows a Hopkinson peak just below the Curie temperature T_C when heating the selected hexagonal and spinel ferrite samples. It is proposed that this peak can be associated with a transition from stable magnetic state to super-paramagnetic relaxation above the blocking temperature up to the T_C. The Hopkinson effect results are compared with SEM micrographs of both studied hexagonal and spinel ferrites.