Thick coatings of barium hexaferrite with the compositions BaFe12O19 and BaCoTiFe10O19 were prepared using high-velocity oxygen-fuel (HVOF) spraying technology. Nanocrystalline precursors embedded in an amorphous matrix were obtained on both Fe and glass-ceramic substrates. To promote the crystallization of the hexaferrites, the coatings were annealed at 800 degrees-1000 degrees C, and single-phase coatings were obtained at 1000 degrees C. The crystallization process was studied with X-ray powder diffraction and with electron microscopy. The magnetic measurements of the coatings were carried out in a static field and at high frequencies. The magnetization of the coatings increased with the annealing temperature to above 50 emu/g for both compositions. The coercivity of BaFe12O19 increased with the annealing temperature to above 2400 Oe, whereas the coercivity of BaCoTiFe10O19 decreased from over 800 Oe, for the as-deposited sample, to 400 Oe for the sample annealed at 1000 degrees C. A minimum 90% absorption was calculated for the BaFe12O19 coatings with thicknesses of 0.15-0.25 mm at around 47 GHz and for the 1-4-mm-thick coatings of BaCoTiFe10O19 at 3-9 GHz.