Magnetic and structural properties of iron-based oxide glasses, Fe 2O3-BaO-B2O3, from 57Fe Mössbauer spectroscopy

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Abstract
57Fe Mössbauer spectroscopy has been combined with bulk results to determine the electronic configuration of iron, the short-range structural order and the magnetic properties of glasses in the system (Fe2O3)x(BaO)y(B 2O3)z. The average coordination of the iron atoms is determined by the Fe/O atomic ratio while the valence state of Fe seems to be affected essentially by the preparation conditions. Structural short-range order around Fe atoms is concluded to be very strong, with random bonding angle and distance fluctuations. At low Fe2O3 content, the glass is paramagnetic down to 1.5 K. Local moment measurements reveal the coexistence of isolated Fe ions and of atomic scale clusters. At intermediate Fe2O3 concentration (~ 25 %), the glass presents a mictomagnetic transition. At large Fe2O3 content (~ 50%), the glass behaves like a superparamagnet, indicating inhomogeneous distribution of the Fe atoms in the solid. Mössbauer spectroscopy is also applied to the investigation of the crystallization of a glass with intermediate Fe2O3 concentration