Determination of the cation site distribution of the spinel in multiferroic CoFe 2 O 4 /BaTiO 3 layers by X-ray photoelectron spectroscopy

Abstract

a b s t r a c tThe properties of CoFe 2 O 4 /BaTiO 3 artificial multiferroic multilayers strongly depend on the crystalline structure, the stoichiometry and the cation distribution between octahedral (Oh) and tetrahedral (Td) sites (inversion factor). In the present study, we have investigated epitaxial CoFe 2 O 4 layers grown on BaTiO 3 , with different Co/Fe ratios. We determined the cation distribution in our samples by X-ray magnetic circular dichroism (XMCD), a well accepted method to do so, and by X-ray photoelectron spectroscopy (XPS), using a fitting method based on physical considerations. We observed that our XPS approach converged on results consistent with XMCD measurements made on the same samples. Thus, within a careful decomposition based on individual chemical environments it is shown that XPS is fully able to determine the actual inversion factor.

Nanostructured spinel cobalt ferrites: Fe and Co chemical state, cation distribution and size effects by X-ray photoelectron spectroscopy

“…The percentage of iron in octahedral sites is thus calculated with the formula %Fe (O h ) ¼ (y  0.5 + (1 À y)  1)  100. 36 The percentage of Fe in octahedral sites calculated following this approach for all the samples ranges between 62 and 64% (Table 3) and it is in very good agreement with the cation distribution formula obtained by 57 4 . On the basis of these results it seems that this curve synthesis based on two symmetric peaks for distinguishing between differently coordinated iron and cobalt is effective to estimate the cation distribution.…”

“…50 The results obtained in this work for Fe 2p are comparable with those obtained for NiFe 2 O 4 : 27 the presence of Fe II can be ruled out since no peaks at about 708 eV and 709 eV 27,50 are observed but nothing can be said about cation distribution. The curve-tting strategy of Co 2p peaks proposed by other authors 36 was thus followed in order to estimate the spinel inversion parameter from XPS data. The estimation strategy starts with distinguishing between Co II in octahedral sites (O h ) and Co II in tetrahedral (T d ) sites on Co 2p peaks ( Fig.…”

“…Binding energy (BE, eV), full width at half maximum (FWHM, eV), energy separation between Co 2p 3/2 and Co 2p 1/2 , fraction of cobalt in octahedral sites (g) and percentage of iron in octahedral sites determined following literature36 Oxygen chemical state plot. Data from this work are reported (black dots) together with data from literature 55 (colored squares).…”

Structure and cation distribution of (Mn0.5Zn0.5)Fe2O4 thin films on SrTiO3(001)

“…For CoFe 2 O 4 and NiFe 2 O 4 , detailed studies about the growth with and without buffer layers on perovskites have been carried out. [12][13][14] It has to be mentioned that these two ferrites crystalize in an inverse spinel configuration in contrast to the Mn 1Àx Zn x Fe 2 O 4 studied here. A detailed review about thin ferrite films has been given by Suzuki in 2001.…”

“…As a matter of fact, the peak ratio of inverse spinel-type CoFe 2 O 4 is reversed to the ones observed in this study. 14 Since XAS is considered to be more sensitive to oxidation states than XPS, 46 those results are discussed now. Previously, the Mn K and Fe K edges have been used to describe the distribution of cations.…”