Precise Mössbauer Parameters of the High Temperature Phase of Fe₃O₄

Mössbauer parameters of the high temperature phase of Fe₃O₄ have been precisely determined as functions of temperature. The measurements were carried out by using a stoichiometric single crystal in applied magnetic field up to 15 kOe. The values of isotropic hyperfine fields and isomer shifts at room temperature for A- and B-sites agree with those of typical 3+ and 2.5+ Fe ions, respectively, while the values of e²qQ/2 and magnetic dipole field for B-site are too small for purely ionic state. The difference between the isomer shifts of A- and B-sites, however, becomes small above around 500-600 K. This corresponds to the contribution of A-site Fe to the electrical conduction above this temperature range. Both the absorption line width and e²qQ/2 value of the B-site spectrum increase noticeably below around 300 K. This is noticed for the first time by our precise measurements. We consider that this feature indicate the change of the electronic states, or the formation of large polarons.