Mössbauer emission spectroscopy study of cobalt-surface-doped acicular magnetite particles

Mössbauer emission spectroscopy was used to study cobalt deposited by alkaline precipitation on the surface of acicular magnetite particles. The samples closely resemble the cobalt-surface-doped particles currently used in magnetic recording tapes. A portion of the cobalt was found to be incorporated into a composition approximating that of cobalt ferrite (CoFe2O4); this is the material responsible for increasing the coercivity of the particles. In samples having 0.33 and 3.3 percent (by weight) deposited cobalt, 85 percent and 34 percent, respectively, of the cobalt was found in CoFe2O4. The cobalt not incorporated into CoFe2O4was found in oxides and hydroxides, mainly in Co(OH)2and (probably) Co3O4. The amount of cobalt found in the form of CoFe2O4is correlated with the increase in coercivity that results from deposition. The possible origins of the uniaxial magnetic anisotropy of surface-doped oxide particles are discussed.