Magnetic phase diagram ofCuGe1−xSixO3

The effect of Si doping on the magnetic properties of the spin-Peierls SP system CuGeO3 was found to differ strongly between polycrystals PC’s and single crystals SC’s. In SC’s, the SP state is suppressed much more strongly, whereas the existence region of the antiferromagnetic AF state is enhanced. We investigated the origin of this difference by means of magnetic susceptibility, specific heat, thermal expansion, Raman scattering, elastic neutron scattering, and x-ray measurements on CuGe1xSixO3 samples prepared under different conditions. The partial oxygen pressure and the temperature during the synthesis were found to have a profound influence on the magnetic properties: preparation under reduced oxygen pressure leads to a stabilization of the AF state, whereas heating above the melting point results in a strong decrease of TSP in Si-doped samples. Therefore, both the AF stabilization and the TSP reduction observed in SC’s are not an intrinsic effect of Si doping PC samples, which can be prepared at lower temperatures and more oxidizing conditions, reflect much better the intrinsic properties of CuGe1xSixO3. We were able to prepare PC samples up to 50 at. % Si and found a continuous decrease of the one-dimensional character of the magnetic properties without pronounced changes in the structure. S0163-18299705321-6