Magnetic phase diagram

WEIDEN, M.; HAUPTMANN, R.; RICHTER, W.; GEIBEL, C.; HELLMANN, P.; KÖPPEN, M.; STEGLICH, F.; FISCHER, M.; LEMMENS, P.; GÜNTHERODT, G.; KRIMMEL, A.; NIEVA, G.

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Lugar: New York; Año: 1997 vol. 55 p. 15067 - 15075

1098-0121

The effect of Si doping on the magnetic properties of the spin-Peierls (SP) system (Formula presented) was found to differ strongly between polycrystals (PCșs) and single crystals (SC"s). In SCșs, 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 (Formula presented)(Formula presented)(Formula presented) 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 (Formula presented) in Si-doped samples. Therefore, both the AF stabilization and the (Formula presented) reduction observed in SCșs 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 (Formula presented)(Formula presented)(Formula presented). 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. © 1997 The American Physical Society.