Incommensurate spin density wave in Co-doped BaFe2As2

TL;DR

This study uses 57Fe Mossbauer spectroscopy to analyze the evolution of magnetic structures in Co-doped BaFe2As2, revealing incommensurate spin density waves at low doping and their temperature-dependent behavior.

Contribution

It provides detailed insights into the incommensurate magnetic modulation in Co-doped BaFe2As2 using Mossbauer spectroscopy, highlighting the transition from commensurate to incommensurate SDW with doping and temperature.

Findings

Incommensurate SDW present at lowest doping level.

Magnetic modulation becomes more sine-wave-like with doping and temperature.

Magnetic hyperfine component persists above SDW transition.

Abstract

57Fe Mossbauer spectroscopy measurements are presented in the underdoped Ba(Fe{1-x}Cox)2As2 series for x=0.014 (T_c < 1.4K) and x=0.03 and 0.045 (T_c ~ 2 and 12K respectively). The spectral shapes in the so-called spin-density wave (SDW) phase are interpreted in terms of incommensurate modulation of the magnetic structure, and allow the shape of the modulation to be determined. In undoped BaFe2As2, the magnetic structure is commensurate, and we find that incommensurability is present at the lowest doping level (x=0.014). As Co doping increases, the low temperature modulation progressively loses its "squaredness" and tends to a sine-wave. The same trend occurs for a given doping level, as temperature increases. We find that a magnetic hyperfine component persists far above the SDW transition, its intensity being progressively tranferred to a paramagnetic component on heating.