Local and collective magnetism ofEuFe2As2

Abstract

We present an experimental study of the local and collective magnetism of EuFe 2 As 2 , that is isostructural with the high temperature superconductor parent compound BaFe 2 As 2 . In contrast to BaFe 2 As 2 , where only Fe spins order, EuFe 2 As 2 has an additional magnetic transition below 20 K due to the ordering of the Eu 2+ spins (J = 7/2, with L = 0 and S = 7/2) in an A-type antiferromagnetic texture (ferromagnetic layers stacked antiferromagnetically). This may potentially affect the FeAs layer and its local and correlated magnetism. Fe-K β x-ray emission experiments on EuFe 2 As 2 single crystals reveal a local magnetic moment of 1.3±0.15 µ B at 15 K that slightly increases to 1.45±0.15 µ B at 300 K. Resonant inelastic x-ray scattering (RIXS) experiments performed on the same crystals show dispersive broad (in energy) magnetic excitations along (0, 0) → (1, 0) and (0, 0) → (1, 1) with a bandwidth on the order of 170-180 meV. These results on local and collective magnetism are in line with other parent compounds of the AFe 2 As 2 series (A = Ba, Ca, and Sr), especially the well characterized BaFe 2 As 2 . Thus, our experiments lead us to the conclusion that the effect of the high magnetic moment of Eu on the magnitude of both Fe local magnetic moment and spin excitations is small and confined to low energy excitations.2

Anisotropic magnetic excitations and incipient Néel order in Ba(Fe1−xMnx)2As2

“…The later is well defined and can be distinguished from the elastic peak at ∆E = 0. In general, RIXS experiments of arsenides unveiled dispersive magnetic excitations, that were found to have nearly isotropic dispersions along the high symmetry BZ directions (π, 0) and (π, π), presenting characteristics that depend weakly on composition [25][26][27][28]. Contrasting with this picture, the RIXS spectra presented in this study display a different behavior as a function of composition.…”

“…These results are surprising since the magnetic excitations observed by RIXS in doped iron arsenides did not show so far any considerable evolution with composition [25][26][27], similarly to what has been found for hole-doped cuprates [31,32]. Thus, for the first time, anisotropic magnetic excitations are observed for iron arsenides by RIXS.…”

Magnetic moment evolution and spin freezing in doped BaFe2As2

“…XES has been established as an extremely sensitive technique in the detection of μ bare 14–16, 43, 45–47, 51, 53–55 . In this spectroscopy a core-electron from the Fe 1 s core-shell is excited into the continuum by a photon (in our case hν  = 7.140 keV), the core-hole is then filled up by a Fe 3 p electron together with the emission of a photon ( hν  = 7.040–7.065 keV), as shown by the scheme in Fig.…”

“…1(b). The relative intensity of these peaks directly depends on the Fe 3 d net spin 14–16, 43, 45–47, 51, 53–55 , and employing a calibration procedure, a quantitative determination of μ bare is possible. This method probes the fs timescale 20 allowing the measurement of μ bare ∝ 〈 S i 〉 and minimizing the problem of electron dynamics decreasing the measured value of the moment.…”

“…These physical entities represent different aspects of magnetism, have different characteristic time and energy scales, and are probed by different experimental techniques 20 . μ bare is detected by local probes such as photoelectron, X-ray absorption, and X-Ray emission spectroscopy 14, 15, 19, 20, 45–47 , whereas μ corr is measured by employing inelastic spectroscopies, such as inelastic neutron scattering 6, 48, 49 and resonant inelastic X-ray scattering 12, 13, 50, 51 .…”