Phase transitions in ilvaite,a mixed-valence iron silicate I. A 57Fe Mössbauer study of magnetic order and spin frustration |
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| Authors: | Kan Xuemin Subrata Ghose B D Dunlap |
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| Institution: | 1. Mineral Physics Group, Department of Geological Sciences, University of Washington, 98195, Seattle, WA, USA
3. Materials Science Division, Argonne National Laboratory, 60439, Argonne, IL, USA
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| Abstract: | Ilvaite, Ca(Fe2+,Fe3+)Fe2+Si2O8(OH) shows two magnetic phase transitions, which have been studied by Mössbauer spectroscopy within the temperature range 120–4 K. The continued charge localization between Fe2+ and Fe3+ ions in octahedral A-sites causes the Fe2+-Fe3+ interaction to be ferromagnetic, although the overall magnetic order is antiferromagnetic. The thermal evolution of the hyperfine fields at the Fe2+ (A) and Fe3+ (A) sites indicates B
hf: 328 and 523 kOe respectively at 0 K and T
N1= 116K. The corresponding values for Fe2+ (B) site are: B
hf 186 kOe and T
N2=36K. An additional hyperfine field exists at the Fe2+(B) site within the temperature range 116–36K due to short-range order induced by the spin ordering in A sites. The considerable difference between the two magnetic transition temperatures is due to spin frustration, because the Fe2+ (B) site occurs on a corner common between two triangles with respect to two sets of Fe2+ (A) and Fe3+ (A) sites with opposite spin directions. |
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