Measurements of the X-band magnetic properties of a series of nickel ferrite-aluminates, as a function of applied magnetic field, are described, together with static magnetization measurements. The results show considerable departures from simple theoretical (Landau–Lifshitz) behaviour, especially in the compensation region of small magnetization, which are probably due to porosity and anisotropy eftects.Resonant-cavity measurements of permeability and permittivity have been made on various nickel ferrite-aluminates and nickel-zinc ferrite aluminates, and compared with transmission measurements for thin slabs of the same materials placed in rectangular waveguide. A general correlation was obtained in all cases, but this was insufficiently precise for exact prediction of waveguide propagation data from intrinsic ferrite parameters. Possible reasons for this are discussed.