New modified M-type ferrite nanoparticles with spinel phase epitaxial overlayer

New modified Fe3O4-Ba(or Sr)Fe12O19 nanoparticles were prepared by using an epitaxial technique for high density magnetic recording. Coercive force reduced from 6.5 kOc of M-type ferrite particles to minimal about 0.2 kOc of modified particles, and saturation magnetization increased from 62.2 to 82.6 cmu/g at the same time. These parameters, H-c, sigma(s), and particle size d, can be easily controlled by changing the content of coating material. The magnetic measurements have shown that the modified particles have an interface coupling between epitaxial layer and core particle. As a result of x-ray diffraction measurements, the reflection intensity of spinel phase increases and that of hexagonal magnetoplumbite phase decreases with the increasing number of Fe2+ ions. The shape of modified particles gradually changes from hexagonal platelike of M-type ferrite particles to square platelike of modified particles. The analysis shows that the Fe2+ ions in suspension directly combined with Fe3+ ions from R-block of core particle to form Fe3O4 layer.