COMPETITION BETWEEN SPIN-PEIERLS PHASE AND 3-DIMENSIONAL ANTIFERROMAGNETIC ORDER IN CUGE1-XSIXO3

The effect of substitution of Si to Ge in CuGe1-xSixO3 single crystals has been studied by magnetic susceptibility, Cu nuclear magnetic reso nance, and neutron scattering measurements. The phase diagram in the ( x,T)-plane is characterized by an initial rapid decrease of the spin-P eierls temperature, T-SP, on increasing x and by the occurrence of a t hree-dimensional long range ordered antiferromagnetic phase at T = T-N in the range 0.005 less than or equal to x less than or equal to 0.05 . This phase diagram is qualitatively discussed. The neutron scatterin g data for x=0.007 show that the dimerization which takes place below T-SP is not suppressed below TN. (C) 1996 American Institute of Physic s.