Magnetic properties of the ternary oxide glasses, Li2O-B2 O3-Fe2O3 from 57Fe Mössbauer spectroscopy

Abstract

57Fe Mossbauer spectroscopy has been combined with bulk magnetic measurements to determine the valence state and coordination of iron as well as the magnetic properties of the ternary oxide glasses, Li2O-B 2O3-Fe 2O3. In all investigated glasses (≤ 8.4 at % Fe), the Fe3+ ions coexist in tetrahedral and octahedral coordinations ; the presence of Fe2+ ions ( < 15 %), which is observed in some glasses, is related to preparation conditions. The magnetic properties of the glasses are governed by the iron content. At low iron concentration (< 3 at %), isolated Fe3+ ions coexist with antiferromagnetic dimers and trimers. At large iron content (3.8 to 8.4 at %) the glasses undergo a mictomagnetic transition to a speromagnetic ordered state. The freezing temperature (Tf), which is frequency dependent, is found to follow a Fulcher law in one sample (5.8 at % Fe) investigated in detail.