A Co2Z hexaferrite composition is provided containing molybdenum and one or both of barium and strontium, having the formula (Ba2Sr(3-Z)Co(2+X))MoxFe(y-2x)O41 where x=0.01 to 0.20; y=20 to 24; and z=0 to 3. The composition can exhibit high permeabilities and equal or substantially equal values of permeability and permittivity while retaining low magnetic and dielectric loss tangents and loss factors. The composition is suitable for high frequency applications such as ultrahigh frequency and microwave antennas and other devices.