Electronic structures and spin states of BaFe2As2 and SrFe2As2 probed by x-ray emission spectroscopy at Fe an

Abstract

Electronic structures of electron-and hole-doped BaFe2As2 and non-doped SrFe2As2 have been studied systematically by x-ray emission spectroscopy at Fe and As K-absorption edges. The electron-and hole-doping causes slight increase of the integrated absolute difference (IAD) values of the Fe Kβ x-ray emission spectra which correlate to the local magnetic moment. Pressure decreases the IAD values and local magnetic moment, and induces the lower-spin states in these compounds. The pre-edge peak intensity of the XAS spectra at the Fe K-absorption edge increases with pressure in both compounds. This indicates an increase of the Fe 3d-As 4p hybridization. It was found that pressure induced a discontinuous increase of the pre-peak intensity of the PFY-XAS spectra at the As K-absorption edge at low pressures in the BaFe2As2 systems. Our results may suggest that the Fe 3d-As 4p hybridization plays a key role in suppressing the AFM order by the doping or pressure and fluctuation of the local magnetic moment and the electron-electron correlation may also play a role on the physical properties of the iron superconductors.

Orbital localization and the role of the Fe and As $4p$ orbitals in BaFe$_{2}$As$_{2}$ probed by XANES

“…To quantify the intensities anisotropy as a function of φ , we fit the Fe K-edge spectra by a Lorentzian (the A 1 peaks) and Gaussian (the A 2 , B, C, D and E peaks) lineshapes plus a Fermi-Dirac function as in figure 3(a). The two peaks in the pre-edge region are clearly present in highresolution experiments [17] and are suggested by the analy-sis of our spectra derivatives. Indeed, adopting two peaks is instrumental to extract a consistent fitting analysis.…”

“…This particular result for the BaFe 2 As 2 parent compound and doped materials is in contrast to the case of SmFeAsO [28]. In addition, as in previous XANES experiments of iron arsenides, the C feature is not much affected by Co substitution [13,14,16,17] and is here shown to be unaffected by Mn substitution as well.…”

“…Hard X-ray absorption spectroscopy (XAS) experiments could provide a handful of key information to the field of the FePns materials, including the role of transition metal substitution on their electronic [13][14][15][16][17][18] and structural properties [19][20][21][22][23][24], as well as the degree of electronic correlations [18,[25][26][27] in these systems. Here, we take advantage of the dipole selection rules dependence on the beam polarization that makes the XAS spectra strongly angular dependent.…”

Espectroscopia de absorção de raios-X dos arseniatos de ferro Ba(Fe>sub<1x>/sub<T>sub<x>/sub<)>sub<2>/sub<As>sub<2>/sub<, (T = Mn, Co, x = 0.0 e x = 0.08)

“…The first relavant piece of finding of this type of experiments, was obtained from Fe K edge experiments. Here, the Fe valence was shown to be robustly +2, under Co doping, pressure or temperature [57,58,59,60]. This constant valence means that there are 6 electrons distributed over the five iron 3d orbitals, and by applying a five-orbital or even threeorbital (d xy , d xz , d yz ) Hubbard model we can have different values for the Hubbard interaction U and Hunds coupling J for each orbital.…”

“…This incites the question as to what happens if one perturbs this tetrahedral coordination in different ways. The answer is that we can drastically change the system macroscopic properties, be chemical substitution at different crystallographic sites in the material crystal structure, or even by applying pressure [57,58,59,60,61,62,63], as Fig. 1.7 shows.…”