We have studied incommensurate spin ordering in single-crystal underdoped ${\text{La}}_{2-x}{\text{Ba}}_x{\text{CuO}}_4$ with $x\sim 0.08$, 0.05, and 0.025 using neutron-scattering techniques. Static incommensurate magnetic order is observed in the ${\text{La}}_{2-x}{\text{Ba}}_x{\text{CuO}}_4$ ($x=0.05$ and 0.025) compounds with ordering wave vectors which are rotated by $45°$ about the commensurate (0.5,0.5,0) position, with respect to that in the superconducting $x=0.08$ material. These spin modulations are one dimensional in the $x=0.05$ and 0.025 samples, with ordering wave vectors lying along the orthorhombic $b^{\ast }$ direction. Such a rotation in the orientation of the static spin ordering as a function of increasing Ba doping, from diagonal to collinear, is roughly coincident with the transition from an insulating to a superconducting ground state and is similar to that observed in the related ${\text{La}}_{2-x}{\text{Sr}}_x{\text{CuO}}_4$ system. This phenomenon is therefore a more generic property of underdoped La-214 cuprates.

• Received 14 August 2008

DOI:https://doi.org/10.1103/PhysRevB.78.092507