SCALING IN DIMER BREAKING BY IMPURITIES IN CUGEO3 - A COMPARATIVE EXPERIMENTAL-STUDY OF ZN-DOPED, MG-DOPED, NI-DOPED, AND SI-DOPED SINGLE-CRYSTALS

We have performed magnetic susceptibility measurements on single cryst als of the doped spin-Peierls system Cu1-xMxGeO3 with M = Zn, Mg, Ni ( 0 less than or equal to x less than or equal to 0.06) and made a compa rison with OUT previous results obtained in CuGe1-ySiyO3 single crysta ls. All these substitutions were found to have three major effects: th e drastic destruction of the spin-Peierls phase, the appearance at low temperature of a three-dimensional antiferromagnetic order, and the f reeing-of some S=1/2 spins. Moreover, doped CuGeO3 shows a universal c haracter for the [T,x(y)] phase diagram and for the doping level depen dence of the proportions of free and dimerized spins, with a scaling f actor x approximate to 3 y. Ni-doping induces a Cu-Ni antiferromagneti c interaction and changes the easy axis in the antiferromagnetic phase .