Barium Hexaferrite Thin Films Prepared by the Sol-Gel Method

Nano-crystalline hexaferrite BaFe₁₂O_(19) (BaM) thin films have been prepared by the sol-gel method. A solution of Ba-nitrate and Fe-nitrates was dissolved in solvent with the stoichiometric ratio Ba/Fe=1/10. Films were spin-coated onto SiO₂/Si substrates, dried and then heated in air at various temperatures. In films prepared at a drying temperature Td=250 ℃ and a crystallizing temperature 650 ℃, single-phase BaM was obtained. High coercivities were obtained in these nano-crystalline thin films, 4~5.5 kOe for hexaferrite. Polycrystalline BaM/SiO₂/Si(100) thin films were characterized by Rutherford backscattering (RBS), thermogravimetry (TGA), differential thermal analysis (DTA), x-ray diffraction (XRD), and vibrating sample magnetometry (VSM), as well as Fourier transform infrared spectroscopy (FTIR). The perpendicular coercivity H_(c⊥) and in-plane coercivity H_(CII) after annealing at 650 ℃ for 2 hours were 4766 Oe and 4480 Oe, respectively, at room temperature, under a maximum applied field of 10 kOe.