ANTIFERROMAGNETIC LONG-RANGE ORDER IN CU1-XZNXGEO3 WITH EXTREMELY LOWZN CONCENTRATION

We have measured the magnetic susceptibilities of single crystals of C u1-xZnxGeO3 with extremely low Zn concentration (x) lower than x=5 x 1 0(-3) at very low temperatures to investigate the spin-Peierls and ant iferromagnetic transitions. The results show that the undoped CuGeO3 h as no antiferromagnetic phase down to 12 mK and there exists an antife rromagnetic long-range order with the easy axis alone the c axis for x down to 1.12(2)x10(-3). The minimum observed Neel temperature was 0;0 285 K for the x=1.12(2)x10(-3) sample. From the concentration dependen ce of the Neel temperature it is concluded that there is no critical c oncentration for the occurrence of the antiferromagnetic long-range or der. This indicates that the dimerization sustains the coherence of th e antiferromagnetic phase of the spin polarization in impurity-doped s ystems and is consistent with the theory of the impurity-doped spin-Pe ierls system. The temperature dependence of the susceptibilities at T> T-N of all samples indicates that the magnetic correlations between lo calized spins are enhanced by a relatively large interchain interactio n of CuGeO3. [S0163-1829(98)51826-7].