Microwave dielectric loss reduction by vacuum treatment for (Ni,Zn,Fe)3O4 films prepared by ferrite plating

Films (~0.5 μm thick) of Ni_0.3Zn_0.4Fe_2.3O₄ were deposited on BN substrates by spin spray ferrite plating from an aqueous solution at 97°C. Exposing the films to vacuum (~0.01 Torr) for 5 hrs at room temperature reduced their dielectric losses, tanδ, from ~0.005 (including losses in the BN substrates) to ~0.002, a value which is indistinguishable from the loss in the substrates. Annealing the films at 300°C in air for 2 hrs also decreased the losses in a similar way, which, however, deteriorated the magnetic characteristics (saturation magnetization, coercive force, and FMR line width) of the films. On the contrary, the vacuum treatment did not deteriorate the magnetic properties at all. The dielectric loss was improved probably because the OH group trapped in the films from the aqueous solution were desorbed by the vacuum or the heat