EFFECTS OF OXYGEN PARTIAL-PRESSURE ON THE CRYSTALLOGRAPHIC STRUCTURE OF MN-ZN FERRITE THIN-FILMS DEPOSITED BY ION-BEAM SPUTTERING

Mn-Zn ferrite thin films were deposited by ion beam sputtering on SiO2 (1000 Angstrom)/Si(100) at various oxygen partial pressures. A single-crystal (110) Mn0.543Zn0.360Fe2.097O4-y disk or a mosaic disk of single-crystal Mn-Zn ferrite with an Fe metal strip was employed as target. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry and low frequency impedance analysis were used to investigate the effects of oxygen partial pressure on the crystallographic structure of Mn-Zn ferrite thin films. The crystal structure of the ferrite film deposited from a single-crystal ferrite target changed from a mixture of the (111) (Mn,Zn,Fe)(1-x)O wustite and the (111) (Mn,Zn,Fe)(3-delta)O-4 spinel phase to a (111) (Mn,Zn,Fe)(3-delta)O-4 single phase with increasing oxygen partial pressure. The ferrite films deposited under an oxygen-deficient condition using the mosaic target had the (111) wustite structure, but the crystal structure changed into the (111) spinel structure with increasing oxygen partial pressure. The crystal structure of the ferrite film changed in a different manner according to the way the oxygen gas was introduced and this can be explained in terms of the crystal structures and the activity of oxygen atoms. The microstructure of the as-deposited him changes from a granular to a columnar microstructure as the crystallographic structure changes from the wustite to the spinel structure with increasing oxygen partial pressure. All the ferrite films, even those with the wustite structure, showed ferrimagnetic characteristics and the resistivity of the films decreased slightly with the crystallographic structural change from the wustite to the spinel.