Magnetic Alignment in $\hbox {REBa}_{2}\hbox {Cu}_{3-{\rm x}}\hbox {Co}_{\rm x}\hbox {O}_{\rm y}$ Compounds

The effects of doping of the cobalt ion on magnetic anisotropy in twinned and orthorhombic YBa₂Cu₃O_y (Y123) were clarified from their magnetic alignment behaviors under a modulated rotating field of 10 T. The cobalt-free Y123 shows two different types of inplane orientation due to the twin microstructure, and the cobalt-doping induced a structural change into a tetragonal phase and conversion of the magnetic hard axis from the b-axis ([100] grain) into a [110] direction ([110] grain). Furthermore, magnetic alignment under a modulated rotating field of 5 T revealed that the inplane magnetic anisotropy of the [110] grains is superior to that of the [100] grain. It is likely that crystallochemical control at the chain site in Y123 promotes the bi-axial orientation using the [110] grains as a grain alignment type for the bi-axial magnetic alignment of twined Y123.