INFLUENCE OF IIA METALS (MG, CA, SR, BA) ON THE CO MODIFICATION OF GAMMA-FE2O3 PARTICLES

In the reaction of Co modification of gamma-Fe2O3, we found a very interesting phenomenon. When cations of Ca2+, Sr2+, or Ba2+ belonging to IIA metals are adsorbed on the surface of gamma-Fe2O3 prior to Co2+ ion adsorption, the coercivity of Co modified gamma-Fe2O3 is significantly increased compared to gamma-Fe2O3 modified only with Co2+. In contrast, when the Mg2+ ion is adsorbed prior to Co2+ ion adsorption, the coercivity is rarely increased. In this paper, we made the following hypotheses in order to interpret these phenomena: (1) Co2+ ions are adsorbed both on the tetrahedral (A) site and the octahedral (B) site in the spinel structure of gamma-Fe2O3. When Co2+ ion occupies the B site and forms cobalt ferrite, the coercivity increases as a result of the surface magnetic anisotropy. (2) Because cations of alkaline earth metals (Ca,Sr,Ba) are easily adsorbed on the A site, adding alkaline earth metal before cobalt addition results in an increase in adsorption selectivity of Co2+ ion on the B site. (3) On the other hand, Mg2+ ion which is easily adsorbed on the B site prevents Co2+ ion occupancy of the B site and as a result the coercivity does not increase.