Abstract
An investigation on the influence of replacement of Fe3+ with Cr3+ on the magnetic properties of BaFe12O19 was made. The specimens BaFe12-x CrxO19 (x=0-3.0) were prepared by the ordinary powder metallurgy method. By X-ray investigation, it was proved that a continuous series of solid solutions of the type BaFe12-xCrxO19 are formed, at least up to x=3.0. The lattice parameter a0 and the volume of the unit cell V0 decreased monotonically with increasing Cr concentration. Curie temperature Tc and the intrinsic coercive force iHc, saturation magnetization Is, and anisotropy constant K, at room temperature were measured for various compositions. The temperature dependence of magnetization was also carried out between the liquid-nitrogen and Curie temperature. These magnetic parameters, except for iHc, decreased monotonically with the increasing amount of substituted ions. But extremely high intrinsic coercive forces under the effect of Cr (iHc=8000 Oe at x=3.0) were obtained. Intrinsic coercive force of the hard ferrites is expected to increase greatly as the particle size varies from multidomain to single domain. The critical radius Rc for single domain particles was calculated for each composition. It becomes larger when the Cr concentration is increased. But from the changes of K and Is against x, the increase in anisotropy field could not be expected. It can then be concluded that single-domain behavior is easily obtained in higher Cr concentration powder, even though under the same milling condition. The similar results can be obtained in case of SrFe12-x CrxO19 (x=0-4.0).
