Neutron diffraction study of the nuclear and magnetic structure of the CrVO4 type phosphates TiPO4 and VPO4

The nuclear structures of TiPO4 and VPO4 have been refined from neutron powder data using the Rietveld technique. For both compounds, the CrVO4 type nuclear structure (Cmcm, Z = 4) was confirmed at 2 K with residuals of R(N) = 0.033 (TiPO4) and R(N) 0.022 (VPO4). In this structure the magnetic ions form chains running along the c-axis. For VPO4, magnetic ordering with a propagation vector k = (1/2 0 0) was found between 2 and 10.3(5) K. This magnetic structure shows antiferromagnetic intra-chain as well as inter-chain ordering. The magnetic moments are aligned parallel to the b-axis and reach the value (mu(exp) = 0.8(1) mu(B). In the temperature range from 10.3(5) K up to the Neel point T-N 25.5(5) K an incommensurate magnetic structure with increasing k(x) component of the propagation vector (0.5 less than or equal to k(x) less than or equal to 0.561) was found. In contrast to the vanadium compound no magnetic ordering was detected for TiPO4 down to 2 K. (C) 1996 Academic Press, Inc.