Spin-density-wave anomaly at 140 K in the ternary iron arsenideBaFe2As2

Abstract

The ternary iron arsenide BaFe2As2 with the tetragonal ThCr2Si2-type structure exhibits a spin density wave (SDW) anomaly at 140 K, very similar to LaFeAsO, the parent compound of the iron arsenide superconductors. BaFe2As2 is a poor Pauli-paramagnetic metal and undergoes a structural and magnetic phase transition at 140 K, accompanied by strong anomalies in the specific heat, electrical resistance and magnetic susceptibility. In the course of this transition, the space group symmetry changes from tetragonal (I4/mmm) to orthorhombic (F mmm). 57 Fe Mössbauer spectroscopy experiments show a single signal at room temperature and full hyperfine field splitting below the phase transition temperature (5.2 T at 77 K). Our results suggest that BaFe2As2 can serve as a parent compound for oxygen-free iron arsenide superconductors.

Magnetic lattice dynamics of the oxygen-free FeAs pnictides: how sensitive are phonons to magnetic ordering?

“…This topic has been already discussed and was extensively studied. Different explanations were proposed ranging from frustration and (a non-observed) lattice distortion to spin fluctuations and effect of lattice-dimensionality (Refs [2,27,35,36,37,38,39] and references therein provide some relevant details on this regards for both measured and calculated magnetic moments in the Fe-pnictides). In the lattice dynamics calculations, in order to determine all inter-atomic force constants, the super cell approach has been adopted [40,41].…”

“…Since then, mainly three types of FeAs-based superconductors have been discovered: RFeAsO [1] (R: Rare earth elements) or AFeAsF (A: alkaline-earth elements), AFe 2 As 2 [2,3,4], and LiFeAs [5]. For 122 compounds the highest Tc was obtained [2,3] in K-doped BaFe 2 As 2 (Tc=38 K). However, a much higher Tc of 56 K and 57.4 K has been found for Sr 0.5 Sm 0.5 FeAsF [6] and Ca 0.…”

“…Structural, electronic and magnetic properties of these compounds are remarkably similar. Structural investigations indicate that these compounds have a tetragonal phase [2,3,10] at room temperature. The parent FeAs pnictides show a well pronounced spin density wave through transitions from the paramagnetic, tetragonal phase to an antiferromagnetically ordered, orthorhombic phase [2,3,10,11].…”

Origin of the dynamics of the spin state in undoped BaFe2As2: Mössbauer studies

“…It seems that there is considerable orbital-dependent reconstruction of the electronic configuration across the magnetostructural transition [4][5][6]. Therefore, unsurprisingly several groups carrying out Mössbauer measurements have observed a singlet at room temperature, characteristic of a paramagnetic compound, and a magnetically split sextet at low temperatures [5,[8][9][10][11][12][13][14][15]. The magnetism is centered on the Fe and not on the Ba or As.…”

“…The literature is replete with observations of well resolved sextets for several other 122 compounds of the form REFe 2 As 2 also, where RE = Eu, Sr or Ca, presumably because of traces of adsorbed O 2 (e.g. [5,[8][9][10][11][12][13][14][15]). …”