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 6.5kOe of M-type ferrite particles to minimal about 0.2kOe of modified particles, and saturation magnetization increased from 62.2 to 82.6emu/g at the same time. These parameters, H_c σ_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.