Spin density wave anomaly at 140 K in the ternary iron arsenide BaFe2As2

TL;DR

This paper reports the discovery of a spin density wave anomaly at 140 K in BaFe2As2, a compound that undergoes structural and magnetic phase transitions, indicating its potential as a parent material for iron arsenide superconductors.

Contribution

It identifies BaFe2As2 as a new parent compound for oxygen-free iron arsenide superconductors with detailed phase transition characteristics.

Findings

SDW anomaly at 140 K in BaFe2As2

Structural transition from tetragonal to orthorhombic

Full hyperfine field splitting below transition

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 (Fmmm). 57Fe Moessbauer 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 new parent compound for oxygen-free iron arsenide superconductors.