During past two decades, hexaferrites, compounds belonging to a large family of magnetic oxides with hexagonal crystal structure and containing iron as the major metallic component, have been found to exhibit gigantic magnetoelectric (ME) effects near room temperature and at low magnetic fields. However, large ME coupling has been realized mainly in single-crystal or polycrystalline forms so far. Despite such great application potentials and timely needs, the synthesis of hexaferrite films of complex structures has not been realized, partly due to complex chemical compositions and a unique crystal structure having long c-axis lattice parameters. Furthermore, as will be demonstrated, optimal final composition can be achieved under limited processing conditions, and to attain the desired purity, off-stoichiometry must usually be found through tedious experimentation.
In the talk, it will be reported a successful growth of X-, Y-, Z-, and U-type hexaferrite thin films on (111)-cut SrTiO3 single crystal substrates by the chemical solution deposition (CSD) method, which is highly cost-effective, operates in an ambient atmosphere, allowing comfortable control over chemical composition and stoichiometry, and thus it is ideally suited for the evaluation of complex material systems or material systems not previously studied in thin-film form. Use of three-dimensional texture analysis and high-resolution X-ray diffraction allow us to study real structure effects and orientation relations between film and substrate, respectively, and their link to the magnetic or ME properties of films. The magnetization process, magnetic domain structure, and anisotropy behavior were investigated using magnetic measurements, Lorentz transmission electron microscopy, and ferromagnetic resonance, respectively. For some cases (Z-type), the results of ME coupling measurements will be mentioned.