In-plane electronic anisotropy in underdoped Ba(Fe1-xCox)2As2 revealed by partial detwinning in a magnetic field

We present results of angle-dependent magnetoresistance measurements and direct optical images of underdoped Ba(Fe1-xCox)(2)As-2 which reveal partial detwinning by action of a 14 T magnetic field. The relative change in the twin domain population for the given field is modest, of order 5-15 %. The associated field-induced hysteretic changes in the resistivity are up to 5% for intermediate Co concentrations, implying a large in-plane resistivity anisotropy in the broken-symmetry state. Based on the generic anisotropic susceptibility of collinear antiferromagnets, we infer a smaller resistivity along the antiferromagnetic ordering direction. The observation of field-induced motion of twin boundaries indicates a substantial magnetoelastic coupling in this material.