Magnetic dipolar and electric quadrupolar effects on the Mössbauer spectra of magnetite above the Verwey transition |
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Authors: | L. Häggström H. Annersten T. Ericsson R. Wäppling W. Karner S. Bjarman |
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Affiliation: | (1) Institute of Physics, University of Uppsala, Uppsala, Sweden;(2) Present address: Department of Mineralogy and Petrology, University of Uppsala, Uppsala, Sweden |
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Abstract: | Mössbauer spectroscopic studies (57Fe) of powdered magnetite have been undertaken between 120 K and 880 K. Below the magnetic transition temperature (TC=839.5 K) three six-line patterns have been fitted to our experimental spectra. The broadening of the B-pattern is explained by two magnetically non-equivalent B-site irons, suggesting broadening due to electron hopping to be negligible. In the paramagnetic state the electric quadrupole splittings of iron at A-and B-sites are found to be constant, independent of temperature, having the values zero and 0.16 mm/s, respectively. The centroid shifts, on the other hand, show above 700 K large deviations from the calculated second order Doppler shift. It is proposed that the deviations arise from a variation in band overlap. The temperature variation of the magnetic fields is found to be proportional to the sublattice magnetization. The difference in the magnetic fields at the two non-equivalent B-sites is measured to be 1.1 T at 310 K. |
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