Magnetic Phase Formation in CoTi-Substituted Ba Hexaferrite Coatings Prepared with Atmospheric Plasma Spraying

Thick coatings of CoTi-substituted Ba hexaferrite with the nominal composition BaCoTiFe10O19 were prepared using atmospheric plasma-spraying technology. The coatings were prepared from prereacted powders of the desired composition. The as-deposited coatings showed a high degree of crystallinity. A detailed investigation of the coatings' phase compositions was conducted with micro-Raman spectroscopy and energy-dispersive X-ray spectroscopy. Two magnetic ferrite phases, CoTi-substituted Ba hexaferrite and Co ferrite, were identified in the coatings. An X-ray powder-diffraction analysis and a quantitative structural analysis based on Rietveld refinement showed that the mass ratio of the two phases and their chemical composition varied with respect to the spraying parameters. Consequently, the static and microwave magnetic properties of the as-sprayed coatings also varied. We were able to explain the formation of the two ferrite phases based on the interplay between the partial melting of the feedstock powder and the recrystallization kinetics.