INCOMMENSURATE MAGNETISM IN PRBA2CU3O6.92

We report resonant x-ray magnetic scattering and high-resolution neutr on-diffraction studies of the Pr site magnetism in high quality single crystals of PrBa2Cu3O6.92. These studies reveal that the Pr sublattic e orders at 19 K in a well correlated, long period incommensurate stru cture with probable wave vector (0.5+/-delta,0.5,0) or (0.5,0.5+/-delt a,0) with delta=0.006 r.l.u. The observed x-ray scattering results fro m dipole transitions, demonstrating the existence of an ordered 5d Pr moment and implying a large 4f moment at the Pr site. A spin reorienta tion transition to a commensurate antiferromagnetic structure of wave vector (0.5,0.5,0.5) is observed at lower temperatures. [S0163-1829(98 )07041 -6].