Effects of deposition and oxidation processes on magnetic and structural properties of iron oxide films

Abstract

Osmium doped (0.75 at.%) iron oxide films were reactively sputter deposited onto Si substrates in an Ar + O2 gas environment. The magnetic and structural properties of the as-deposited films depend critically on deposition process parameters such as 02 flow rate, chamber pressure, substrate temperature, RF power and substrate rotation speed. The deposition process window has been determined for which only the spinel structure was observed. X-ray diffraction indicated films grown at a low O2 flow rate of 3.0 sccm and a substrate temperature of 230°C had more random orientation and a lattice parameter closer to that of the bulk Fe304 value. This condition produced a high saturation moment of 410 emu/cc. Increasing O2 flow rate induced preferential (111) orientation and decreased the lattice parameter of the film. In some instances at higher O2 flow rate, γ-Fe203 superlattice structure peaks were also observed, indicating the presence of the γ-phase in the as-deposited films. As 02 flow rate was increased, the Ms decreased while Hcand S* increased. Rutherford backscattering also confirmed that O/Fe ratio in the film increased as the O2 flow rate was increased. For a fixed O/Fe ratio in the film, decreasing the substrate temperature increased the lattice parameter beyond that of the bulk Fe304 value. Both Ms and S* decreased. The grain size, as observed by TEM, also decreased with substrate temperature. Therefore, while operating in this spinel structure window, the exact stoichiometry, structural and magnetic properties of the films depend critically on the process parameters. Oxidation of the iron oxide films toward y-phase was carried out in air at temperatures between 200 and 330°C. Coercivity and S* increased but Ms decreased after oxidation. Films deposited at higher O2 flow condition tend to form α-Fe203 at lower oxidation temperature and/or shorter oxidation time. Thus, to avoid the α-Fe2O3 formation, the proper oxidation conditions need to be selected according to the initial deposition conditions. © 1987 IEEE