Remarkable difference in the effects of nonmagnetic impurities on the Haldane and spin-Peierls systems

We have observed a remarkable difference in the impurity effects on the Haldane and spin-Peierls (SP) systems, ${\mathrm{NiC}}_2$ ${\mathrm{O}}_4$⋅2DMIZ (DMIZ is dimethyl imidazole) and ${\mathrm{CuGeO}}_3$, by measuring the high-field magnetization and temperature dependence of the susceptibility. The Haldane state survives even in the heavily doped sample with a nonmagnetic impurity concentration of 20%. On the other hand, the SP state almost disappears in the lightly doped sample with an impurity concentration of 4%. The physical significance of these results is discussed.