⁵⁷Fe Mössbauer spectroscopy on iron based pnictides and chalcogenides in applied magnetic fields

Abstract

In this article, we show possibilities and limitations of the 57Fe‐Mössbauer spectroscopy applied to iron‐based pnictides and chalcogenides. The principle structure of these materials are FePn‐ or FeCh‐layers with tetragonally coordinated Fe2+ ions. These layers are the electronically active structures for the competing magnetic and superconducting ground states. Mössbauer spectroscopy is frequently applied to investigate zero field local magnetic properties of both powder and single crystal materials. However, the absolute size of the hyperfine parameters often is small and the study can benefit from the application of an external field. With the help of an applied field it is possible to study magnetic interactions, ferromagnetic impurities, the sign of the electric field gradient (EFG) and magnetoelastic coupling. We show different aspects of applied magnetic field measurements and discuss results in iron‐based pnictides and chalcogenides. The field distribution induced by applied fields is in the ideal case described by exchange and anisotropy fields. Due to sample inhomogeneity, a model independent analysis can be necessary as in case of our LaFeAsO transverse field measurements.

Suppression of the magnetic order in CeFeAsO: Nonequivalence of hydrostatic and in-plane chemical pressure

“…However, it was shown that in the LaFeAsO-based compounds V zz is positive. 39,40 In the magnetic phase we obtained a pos-itive V zz value and thus we are confident that this is also the case in the paramagnetic phase of the CeFeAsO series.…”

Magnetism and site exchange in CuFeAs and CuFeSb: A microscopic and theoretical investigation

“…The conversion ratio of Mössbauer hyperfine field and magnetic moment determined from neutron diffraction is −10 T/μ B . This is less than the typical value of iron arsenides/chalcogenides [40], approaching the value of −13 T/μ B for a predominant core contribution [67], which is typically observed in more localized systems. The localization-or reduced covalencycaused by the large Fe-Sb bond distance of 2.69Å [24] becomes apparent with regard to the Mössbauer isomer shift δ(T → 0) = 0.63 mm/s with respect to room temperature iron, which is 0.1 mm/s more than CuFeAs, amongst many other iron arsenides.…”

“…2 inset, Fig. 3) with a quadrupole splitting (Table II) typical for 122 compounds [40]. Below 11 K it broadens by ≈0.1 mm/s.…”

“…For both samples the broadening starts at ≈11 K and almost linearly increases down to 5 K, below which the curve slightly flattens. The broadening corresponds to a hyperfine field B hyp ≈ 1 T. Assuming an iron pnictide specific conversion ratio of 6.7 T/μ B [40], this corresponds to a magnetic moment of 0.15 μ B . This value is somewhat lower than the saturation moment between 0.2 and 0.3 μ B /Fe, which the magnetization measurements suggest [26,27].…”

Tuning Fe–Se Tetrahedral Frameworks by a Combination of [Fe(en)3]2+ Cations and Cl– Anions

“…The second component, Q2, has δ of 1.13 mm/s and ∆ΕQ of 1.80 mm/s, which are characteristic values for high-spin Fe 2+ . 45 This component has an intensity of 56% and a linewidth of 0.49 mm/s.…”