Antiferromagnetic phase in Zn- and Ni-doped CuGeO3

The magnetic susceptibility of single crystals Cu1−x M x GeO3 (M=Zn, Ni) were investigated to study the effects of impurities on the inorganic spin-Peierls material CuGeO3. We succeeded in the growth of Zn-doped single crystals with 0.007≤x≤0.09 and Ni-doped ones withx=0.033. We determined temperature vsx phase diagram of the Zn-doped single crystals, which is almost identical to that of the polycrystaline samples. In both Cu1−x Zn x GeO3 and Cu1−x Ni x GeO3, the antiferromagnetic transition occurs below 5 K. It is proved that the easy axis of Ni-doped CuGeO3 is nearly along thea axis, while that of Zn-doped CuGeO3 is along thec axis as previously reported. This difference of spin orderings between Zn-doped and Ni-doped CuGeO3 is caused by that Ni2+ ions carry spinS=1 while Zn2+ ions are nonmagnetic.