Mössbauer studies of the peculiar magnetism in parent compounds of the iron-based superconductors

Abstract

A review of the magnetism in the parent compounds of the iron-based superconductors is given based on the transmission Mössbauer spectroscopy of 57 Fe and 151 Eu. It was found that the 3d magnetism is of the itinerant character with varying admixture of the spin-polarized covalent bonds. For the '122' compounds a longitudinal spin density wave (SDW) develops. In the case of the EuFe 2 As 2 a divalent europium orders antiferromagnetically at much lower temperature as compared to the onset of SDW. These two magnetic systems remain almost uncoupled one to another. For the non-stoichiometric Fe 1+x Te parent of the '11' family one has a transversal SDW and magnetic order of the interstitial iron with relatively high and localized magnetic moments. These two systems are strongly coupled one to another. For the "grand parent" of the iron-based superconductors FeAs one observes two mutually orthogonal phase-related transversal SDW on the iron sites. There are two sets of such spin arrangements due to two crystallographic iron sites. The FeAs exhibits the highest covalency among compounds studied, but it has still a metallic character.

Mössbauer study of Eu0.57Ca0.43Fe2As2 and Eu0.73Ca0.27(Fe0.87Co0.13)2As2: A comparison to ‘122’ iron-based superconductors parent compounds EuFe2As2 and CaFe2As2

“…Mössbauer spectroscopy is very useful while looking at the peculiar magnetism of parent compounds [15][16][17] and iron-based superconductors [18][19][20]. The present contribution reports Mössbauer results obtained by means of 57 Fe and 151 Eu spectroscopy on the Eu 0.57 Ca 0.43 Fe 2 As 2 compound being iso-electronic with compounds EuFe 2 As 2 and CaFe 2 As 2 [21].…”

Synthesis, crystal structure and magnetism of Eu3Sc2O5Fe2As2

“…The 57 Fe spectrum of Eu 3 Sc 2 O 5 Fe 2 As 2 shows a single signal with isomer shifts of 0.35 (1) (intermetallic iron [32,38,39]) at ambient temperature and 78 K, respectively, and a small interaction between quadrupole and electric field gradient resulting in a splitting of 0.20(1) mm s -1 .…”

Transition to collapsed tetragonal phase inCaFe2As2single crystals as seen byFe57Mössbauer spectroscopy

“…in FeAs grown CaFe 2 As 2 single crystals quenched from 960 • C), using experimental techniques that are either difficult or impossible to combine with hydrostatic pressure. [19][20][21][22][23][24] and related materials, [25][26][27][28][29] including Sn-grown CaFe 2 As 2 single crystals 6,30,31 and powdered single crystals 32 primarily for probing magnetism (although it should be noted that grinding of CaFe 2 As 2 affects the macroscopic and microscopic magnetic properties 33 ). In this work we will use this local probe technique to perform a detailed temperature-dependent study of the cT transition (and the cT phase) in single crystals of undoped, FeAs-grown 960 • C quenched 15 , CaFe 2 As 2 .…”

“…• and related materials, [25][26][27][28][29] The isomer shift and the quadrupole splitting observed in Mössbauer spectroscopy can be directly related to the electron density at the nucleus and the electric field gradient respectively, both of which can be calculated in the framework of ab-initio Density Functional…”