EFFECTS OF ANNEALING ON THE MICROWAVE PROPERTIES OF SPIN-SPRAY NI-ZN FERRITES

We have studied the properties of a series of spinel ferrite thin films prepared from aqueous solutions at temperatures slightly below 100 degrees C, for a range of compositions from pure Fe3O4 to about Ni.34Zn.18Fe2.48O4. As made, the films are semiconducting and have high dielectric losses, but have narrow ferromagnetic resonance linewidths and often display standing spinwave spectra. As a result of annealing in air at temperatures above 300 degrees C, these ferrites undergo a transformation to a State having much higher resistivity and a reduced magnetic moment compared to as-grown films. This annealing decreases the microwave dielectric losses. but increases the ferromagnetic resonance linewidth. The changes in these properties with annealing are consistent with a partial transformation from spinel to maghemite, gamma-Fe2O3.