Incommensurate spin density wave in Co-doped BaFe ₂ As ₂

Abstract

57Fe Mossbauer spectroscopy measurements are presented in the underdoped\nBa(Fe{1-x}Cox)2As2 series for x=0.014 (T_c < 1.4K) and x=0.03 and 0.045 (T_c ~\n2 and 12K respectively). The spectral shapes in the so-called spin-density wave\n(SDW) phase are interpreted in terms of incommensurate modulation of the\nmagnetic structure, and allow the shape of the modulation to be determined. In\nundoped BaFe2As2, the magnetic structure is commensurate, and we find that\nincommensurability is present at the lowest doping level (x=0.014). As Co\ndoping increases, the low temperature modulation progressively loses its\n"squaredness" and tends to a sine-wave. The same trend occurs for a given\ndoping level, as temperature increases. We find that a magnetic hyperfine\ncomponent persists far above the SDW transition, its intensity being\nprogressively tranferred to a paramagnetic component on heating.\n