Stoichiometry ofFe3−δO4(111)ultrathin films on Pt(111)

Abstract

The composition and magnetic properties of two types of ultrathin ${\mathrm{Fe}}_{3\ensuremath{-}\ensuremath{\delta}}{\mathrm{O}}_{4}(111)$ films grown epitaxially on Pt(111) have been characterized using conversion electron M\"ossbauer spectroscopy (CEMS) and x-ray magnetic circular dichroism (XMCD). CEMS data from both films indicate that the magnetic moments lie in-plane and that a paramagnetic contribution is present that is not seen in spectra of bulk magnetite samples. The XMCD results are in good agreement with theoretical calculations, enabling the stoichiometry of the films to be determined as ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ and ${\mathrm{Fe}}_{2.91}{\mathrm{O}}_{4}.$ The concentrations of both the tetrahedral ${\mathrm{Fe}}^{3+}$ and octahedral ${\mathrm{Fe}}^{2+}$ ions are reduced in the nonstoichiometric film, the decrease in the tetrahedral site probably being due to disorder. CEMS consistently yields a high tetrahedral:octahedral ratio of about 0.7:1, probably because of a contribution from a nonstoichiometric FeO interface layer.