Fe57Mössbauer study of chromium-doped magnetite,Fe3−xCrxO4(0≤x≤0.5) above the Verwey transition

Abstract

$^{57}\mathrm{Fe}$ M\ossbauer measurements show that the ratio of the integrated intensities of the $^{57}\mathrm{Fe}$ $A$- and $B$-site M\ossbauer subspectra is in good agreement with those expected for the cation distribution $({\mathrm{Fe}}^{3+})({\mathrm{Fe}}_{1\ensuremath{-}x}^{3+}{\mathrm{Fe}}^{2+}{\mathrm{Cr}}_{x}){\mathrm{O}}_{4}$, $0\ensuremath{\le}x\ensuremath{\le}0.3$. The magnetic moments are also found to be in good agreement with this cation distribution. The compositional dependences of the M\ossbauer hyperfine parameters display no features in this compositional range that would result from a qualitative change in electronic structure. The observed line broadening and line shapes are readily accounted for by the local configurations of ions resulting from a random substitution of ${\mathrm{Cr}}^{3+}$ on the $B$ sites. Consequently, the conduction mechanism in these doped magnetites is similar to that in pure ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$. The marked changes in the spectra for $x\ensuremath{\approx}0.5$ are due primarily to the commencement of the occupation of the $A$ site by ${\mathrm{Fe}}^{2+}$ ions and the change of the M\ossbauer parameters between $x=0.3$ and $x=0.5$ are as expected if $A$-site ${\mathrm{Fe}}^{2+}$ ions are present.