MAGNETIC-STRUCTURE OF ANTIFERROMAGNETIC PDCRO2 POSSIBLE DEGENERATE HELICES ON A RHOMBOHEDRAL LATTICE

Neutron powder diffraction was measured on PdCrO2 which has a rhombohe dral lattice of Cr3+ ions. The observed magnetic scattering forms a ra ther broad bump with peaks at (1/3 1/3 l) indicating the 120 degrees m agnetic structure in a triangular lattice c-plane. The magnetic moment s of 2 mu(B) lie in the c-plane and T-N was found to be 40 K. Magnetic diffuse scattering is appreciable even at 150 K. The magnetic peak ha s an asymmetric saw-tooth profile toward the high-Q side implying that the stacking of the 120 degrees structure is distributed as expected in ''degenerate helices'' proposed for the rhombohedral antiferromagne t.