Effects of preparation conditions on the hysteresis behavior of granular Fe-SiO2

The hysteresis behavior of Fe-x(SiO2)(1-x) granular films was studied as a function of preparation conditions. The films were prepared by de and rf magnetron sputtering over the composition range of x(u)psilon = 0.1-0.9, where x(u)psilon is the volume fraction of Fe. The tandem and composite target deposition methods, both with and without titanium presputtering, were used to prepare the films. Typical granular structure was observed in these films, with grain size in the range of 2-20 nm. X-ray diffraction and selected area diffraction showed a bcc alpha-Fe-type structure. Magnetic measurements showed that by varying the deposition method and some of the sputtering parameters including sputtering rate, argon flow, film thickness, and substrate temperature, it is possible to switch from a relatively magnetically hard sample (H-c similar to 650 Oe) to a soft sample (H-c similar to 20 Oe). For the former sample, a dramatic increase in H-c has been observed at cryogenic temperatures. This result, along with the Mossbauer data, suggest a shell/core granule morphology with an Fe and/or Fe-Si core surrounded by an Fe-Si-O phase. (C) 1997 American Institute of Physics.