Electrical and magnetic properties of cronstedtite |
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| Authors: | J M D Coey T Bakas C M McDonagh F J Litterst |
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| Institution: | 1. Department of Pure and Applied Physics, Trinity College, 2, Dublin, Ireland
3. Physics Department E 15, Technical University of Munich, D-8046, Garching bei München, West Germany
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| Abstract: | Two samples of cronstedtite, a mixed valence serpentine with ideal formula {Fe 2 2+ ,Fe3+}Si,Fe3+]O5(OH)4, have been examined by X-ray and neutron diffraction, thermopiezic analysis, magnetization and susceptibility measurements and Mössbauer spectroscopy. The conductivity is thermally activated, with activation energies of 0.25 eV in the basal plane and 0.37 eV in the perpendicular direction. The shape of paramagnetic Mössbauer spectra above 200 K is influenced by charge fluctuations in octahedral sites and fits of spectra at temperatures up to 410 K with a stochastic relaxation model give an activation energy of 0.19 eV. Static charge ordering sets in progressively below about 100 K. Cronstedtite orders antiferromagnetically below 12 K in a structure with antiferromagnetic octahedral sheets and moments perpendicular to the a-axis. Magnetic and charge-ordered structures are proposed for the ideal composition. |
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