Critical behavior of the spin density wave transition in underdoped Ba(Fe1−xCox)2As2 (x≤0.05): As75 NMR investigation

We investigate the nature of the SDW (spin density wave) transition in the underdoped regime of an iron-based high-Tc superconductor Ba(Fe1−xCox)2As2 by As75 NMR, with primary focus on a composition with x=0.02 (TSDW=99 K). We demonstrate that critical slowing down toward the three-dimensional SDW transition sets in at the tetragonal to orthorhombic structural phase transition Ts=105 K, suggesting strong interplay between structural distortion …