Magnetic structure of La_1.2Tb_0.8CuO₄

A high-intensity powder neutron diffraction study of La_1.2Tb_0.8CuO₄ which has the tetragonal T*-structure shows that the compound orders antiferromagnetically with a magnetic structure which can be described by employing a magnetic propagation vector, τ = (-1/2, 1/2, 0) perpendicular to the Cu²⁺ spin direction, S = (1/2, 1/2, 0) (identical to that of La₂CuO₄). The staggered Cu²⁺ moment at 1.6 K is 0.46 (6) μ_B. However, non-collinear spin structures are also possible. The appearance of magnetic diffuse scattering at low temperatures is interpreted as the signature of short range magnetic ordering of the Tb³⁺ ions. Essentially unchanged magnetic behaviour is found in the lightly-doped La_1.19Tb_0.8Sr_0.01CuO₄ and La_1.2Tb_0.79Ce_0.01CuO₄ materials.