The local structure and magnetic correlations in La(Fe1-Mn )AsO system

Mn substitution effect on the local structure of La(Fe1−x Mn x )AsO studied by temperature dependent x-ray absorption measurements

“…It is known that electronic and magnetic properties of ironpnictides are largely determined by the FeAs 4 tetrahedrally coordinated layer [13][14][15][16] and hence a direct chemical substitution in this layer has been very intriguing. In particular, transition metal substitutions at the Fe site are widely studied [7-9, 11, 17, 18], and among them the Mn substitution shows a peculiar behavior by triggering a drastic suppression of the nematic transition and the long-range magnetic ordering [18][19][20] for a very small concentration of ∼0.2%.…”

“…This effect of Mn substitution is typical to (RE)FeAsO (RE = rare Earth) and other pnictide families, e.g., BaFe 2 As 2 [21][22][23]. In La(Fe 1−x Mn x )AsO, Mn substitution induces a decrease in the Néel temperature (T N ) and the magnetic order changes from long-range to short-range for x ∼ 0.02, that is intimately related with the corresponding FeAs layer thickness [16,19]. Recently, a complex structural phase diagram has been also proposed for La(Fe 1−x Mn x )AsO [20] with formation of static CDW for x 0.02 [24].…”

“…Also, there is no signature of spin fluctuations in LaFe 1−x Mn x AsO 1−y F y , studied by muon spin resonance (μSR) measurements. On the other hand, x-ray emission spectroscopy experiments on an undoped La(Fe 1−x Mn x )AsO have revealed that appearance of local Fe magnetic moment by Mn substitution should have some important role [16]. The second hypothesis is based on Mn acting as an impurity scattering center that causes electron localization.…”

“…In this context, the local structure analysis can be important for exploring possible atomic displacements that may have the driving role. In our earlier work we have reported [16] local structure investigations on La(Fe 1−x Mn x )AsO by a combined analysis of As K-edge and Fe K-edge extended x-ray absorption fine structure (EXAFS) measurements, performed at room temperature. In addition, we have discussed the Fe local magnetic moment, measured by Fe K β x-ray emission spectroscopy, in relation to the magnetic order and the arsenic height (As-height) from the Fe-Fe plane as a function of Mn substitution.…”

The CLEAR X-ray emission spectrometer available at the CLAESS beamline of ALBA synchrotron

“…In the next examples, XAS and XES measurements collected at CLAESS are coupled to investigate Fe-based superconductors. In the first work, the results highlight how the suppression of super-conducting transition temperature by Mn substitution in the fluorine-doped LaFeAsO is likely to be due to the competing Fe local magnetic moment (directly quantified by XES) and long-range magnetic correlations (Hacisalihoglu et al, 2019). In the second, temperature-dependent Fe K-edge XAS and complementary Fe K XES results obtained on a self-doped CaKFe 4 As 4 superconductor reveal that both the anion height [red symbols in Fig.…”