Effect 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 x(v) = 0.1-0.9 volume fraction of Fe. The Tandem deposition method and deposition from a composite target both with and without titanium sublimation, were used to prepare the films. A typical granular structure was observed, with grain size in the range 2-20 nm. X-ray diffraction and selected area diffraction showed an alpha-Fe (bcc) type structure. Magnetic properties showed that by varying the deposition method and some of the sputtering parameters (sputtering rate, argon flow, film thickness and substrate temperature), it is possible to switch from a relatively magnetically hard sample (H-c similar to 700 Oe) to a soft sample (H-c similar to 20 Oe). A dramatic increase in H-c has been observed at cryogenic temperatures. This result, along with the Mossbauer data, suggests a shell/core granule morphology with an Fe and/or (Fe-Si) core surrounded by Fe-Si-O.