Effect of preparation technique on the structural and magnetic properties of granular Fe‐SiO2 (abstract)

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Abstract
Previous studies have shown that large coercivities, exceeding 2 kOe, can be obtained in Fe‐based ceramic granular films. The coercivities were also found to be sensitive to the type of matrix material used, being higher in the SiO2 matrix. In this study the hysteresis behavior of FeX(SiO2)1−X granular films was studied as a function of the preparation technique. The films were prepared by dc magnetron sputtering over the composition range of xv=0.1–0.9 volume fraction of Fe. Tandem deposition both with and without titanium sublimation, and deposition from a composite target were used in preparing the films, which resulted in different oxygen environments. Coercivity measurements were found to be strongly composition dependent, with maximum values up to 700 Oe at xv≊0.5 of Fe, for all sets of samples. Typical granular structure was observed, with grain size in the range of 5–20 nm, with the smaller size obtained from composite targets. X‐ray diffraction and selected area diffraction showed a structure of a‐Fe (bcc). Thermomagnetic curves showed a peak which can be associated with the onset of superparamagnetism. By varying the deposition method and the oxygen environment, we were able to switch from a relatively magnetically hard sample (Hc∼500 Oe) to a soft sample (Hc∼20 Oe). Mossbauer data are being analyzed to determine the presence of any oxides, their magnetic state and their effect on hysteresis.

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