Microwave properties of low-saturation-magnetisation nickel-gallium-aluminium ferrites

Because of the possibility of their application at low (S and C band) microwave frequencies, a study has been made of the low-saturation-magnetisation ferrites of the system NiGaxAlyFe2¿(x + y)O4. The appropriate magnetic and microwave properties have been measured for a group of polycrystalline specimens of this type having saturation magnetisations ¿800Gs, and the effect of the preparation conditions on this type of material has been investigated. It is found that low-field microwave loss persists at frequencies of about 3000 Mc/s even for specimens with a saturation magnetisation of about 730Gs, this loss being caused, possibly, by a broad domain-wall resonance. Although other properties appear satisfactory for microwave applications, it is concluded that, at best, these materials will be useful in the frequency range above 4000 Mc/s.