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.