Antiferromagnetic domains in YBa 2 Cu 3 O 6 + x probed by Gd 3 + ESR (original) (raw)

The anisotropy of the static homogeneous magnetic spin susceptibility of the antiferromagnetic CuO 2 bilayers and the crystal-field parameters are measured in Gd-doped YBa 2 Cu 3 O 6ϩx ͑small x͒ single crystals using Gd 3ϩ ESR at 9, 75, 150, and 225 GHz. We show that the easy magnetization direction is along ͓100͔ and that there is a magnetostriction leading to an orthorhombic lattice distortion. We observe an antiferromagnetic domain structure corresponding to the two equivalent orthorhombic distortions of the tetragonal lattice which depends on magnetic fields of the order of 1 T. The domain structure is unchanged between 10 and 150 K and is independent of thermal and magnetic history. We discuss two models: ͑i͒ charged domain walls, ͑ii͒ magnetization pinned to a small number of defective oxygen-rich Cu͑1͒ layers.