Hexaferrite thin films of Ba1-xRxFe12-xNixO19 (R=Pr, La) were grown on nonmagnetic garnet substrates by rf sputtering. When deposited at a substrate temperature of 550 °C at rf power density (PDrf) larger than 19 W/cm2, the films were completely crystallized, with the c axis preferentially oriented normal to the film plane. Transmission electron microscopy revealed that the films deposited at low PDrf were amorphous but locally contained microcrystallites several nm in size. On the other hand, the films deposited at PDrf larger than 20 W/cm2 were polycrystalline with a crystallite size as large as 300 nm. Faraday rotation measurements showed that the Ni substitution induced a large negative rotation in the photon energy range of 2.1–2.6 eV. This Ni contribution was predominantly attributed to the crystal-field transition of octahedrally coordinated Ni2+ ions lying in the 2 eV range. No contribution by Pr3+ ions to the Faraday rotation was observed within the photon energy range measured. © 1997 American Institute of Physics.