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Ferromagnetic or antiferromagnetic Fe III spin configurations in sheet silicates |
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| Authors: | M G Townsend G Longworth C A M Ross R Provencher |
| Institution: | 1. Department of Energy, Mines and Resources, K1A 0G1, Ottawa, Canada 2. Harwell Laboratory, Oxfordshire, UK 3. British Geological Survey, Nottingham, UK |
| Abstract: | Mössbauer spectra of glauconite and nontronite recorded at temperatures down to 1.3K and in applied fields up to 4.5 T show that Fe III spin configurations are respectively ferromagnetic and antiferromagnetic. It is shown that in a particular material depending on the distribution and concentration of Fe III in the silicate sheet either mode might occur. A new model of competing nearest-neighbour (J 1) and next-nearest-neighbour (J 2) magnetic exchange interactions in the triangular lattice is introduced to account for the results. From available magnetic susceptibilities we estimate ∣J 1∣～6∣J 2∣. The results lead to the conclusion that the Fe III cations are highly ordered in glauconite and occupy cis sites so as to maximize their mutual separations. |
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