Liquid phase deposition of barium hexaferrite thin films

In this study we demonstrate for the first time that magnetic films with a complex crystal structure, such as hexagonal barium ferrite BaFe ₁₂O₁₉, can be successfully fabricated in aqueous solutions at 60 C by the liquid phase deposition method (LPD). Highly uniform films with a variable thickness were deposited on (001) Si substrates at 60 C and analyzed by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and magnetic force microscopy. As expected, the as-deposited films are amorphous and consist of a mixture of metal oxide/oxyhydroxide intermediates which can be converted into the desired hexagonal barium ferrite phase upon heat treatment at 950 C in air. The molar ratio of the metal cations in the treatment solution was found to play a crucial role on the composition of the films, with chemically pure BaFe₁₂O₁₉ films forming in solution when the Fe³⁺/Ba²⁺ molar ratio is n = 11. The films are constructed by close-packed spheroidal particles and have out-of-plane coercive fields which increase from 134.9 to 215.7 kA/m when their thickness varied from 100 to 524 nm. The in-plane coercivity values are slightly smaller than the out-of-plane coercivity, indicating the existence of a randomly oriented magnetic anisotropy. With their easy preparation and magnetic properties comparable to those of the bulk materials, these structures are of interest for implementation in data storage and microwave applications.