MAGNETIC-STRUCTURE OF LA1.2TB0.8CUO4

A high-intensity powder neutron diffraction study of La1.2Tb0.8CuO4 wh ich has the tetragonal T-structure shows that the compound orders ant iferromagnetically with a magnetic structure which can be described by employing a magnetic propagation vector, tau = (1/2, 1/2, 0) perpendi cular 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) mu(B). Ho wever, 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. Essen tially unchanged magnetic behaviour is found in the lightly-doped La1. 19Tb0.8Sr0.01CuO4 and La1.2Tb0.79Ce0.01CuO4 materials.