- Studies of the microwave properties of Ni-based inverted ferromagnetic opals in the 2 – 20 GHz frequency band, backed by static characterization relying on SQUID measurements of remagnetization process, have been carried out. A theoretical model based on an array of weakly magnetically coupled, through dipolar interactions, ferromagnetic cylinders oriented along the preferred crystallographic directions, has been proposed. It satisfactorilly explains, both qualitatively and qualitatively, major experimental results.