The optical and magneto-optical properties of single crystal Co/Ti doped barium hexaferrites have been measured over the wavelength range 400–800 nm. The spectral dependencies of the Kerr effect indicate that at short wavelengths Fe3+, and at long wavelengths Co2+ ions, are responsible for the M.O transitions. In the near IR, and after quadrilayer enhancement, heavily doped ferrite performs better than TbFeCo as an M.O recording medium.
Atkinson, R., Gerber, R., Papakonstantinou, P., & Zimsa, Z. (1992). Optical and magneto-optical properties of Co/Ti substituted barium ferrite. Journal of Magnetism and Magnetic Materials, 104-10, 1005-1006. https://doi.org/10.1016/0304-8853(92)90462-W