SPIN DYNAMICS IN PURE AND ZN-DOPED CUGEO3 BY MUON SPIN RELAXATION - SPIN-PEIERLS AND SPIN-GLASS TRANSITIONS

Zero and longitudinal muon spin relaxation has been used to characterize the spin dynamics of local magnetic moments in the quasi-one-dimensional S = 1/2 cuprates CuCeO3 and Cu0.96Zn0.04GeO3. Frozen moments are not observed in CuGeO3, only a slowing down of the fluctuating rate of Cu moments was seen below 14 K. Magnetic measurements in the slightly doped sample confirm the suppression of the spin-singlet transition, and the appearance of hysteresis between the zero-field-cooled and field-cooled branches of the magnetic susceptibility below T approximate to 4.5 K, both absent in the pure compound. The depolarization of muons gives evidence of the appearance of randomly frozen Cu moments in the doped compound below T-g approximate to 4.5 K. The dynamic relaxation rate lambda(d) is appreciably higher around T-g than below 4 K, and the correlation time tau(c) of the magnetic fluctuations of 3d Cu moments in Cu0.96Zn0.04GeO3 is estimated to be tau(c) approximate to 10(-8) s at 5 K.