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 film s prepared from aqueous solutions at temperatures slightly below 100 d egrees C, for a range of compositions from pure Fe3O4 to about Ni.34Zn .18Fe2.48O4. As made, the films are semiconducting and have high diele ctric losses, but have narrow ferromagnetic resonance linewidths and o ften display standing spinwave spectra. As a result of annealing in ai r at temperatures above 300 degrees C, these ferrites undergo a transf ormation to a State having much higher resistivity and a reduced magne tic moment compared to as-grown films. This annealing decreases the mi crowave dielectric losses. but increases the ferromagnetic resonance l inewidth. The changes in these properties with annealing are consisten t with a partial transformation from spinel to maghemite, gamma-Fe2O3.