Incommensurate spin density wave in Co-doped BaFe₂As₂

CEA, Centre de Saclay, DSM/IRAMIS/Service de Physique de l'Etat Condensé 91191 Gif-sur-Yvette, France, EU

Corresponding author: pierre.bonville@cea.fr

Received: 16 December 2009
Accepted: 16 March 2010

Abstract

⁵⁷Fe Mössbauer spectroscopy measurements are presented in the underdoped Ba(Fe_1-xCo_x)₂As₂ series for x = 0.014 (T_c < 1.4 K) and x = 0.03 and 0.045 (T_c 2 and 12 K, 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.