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 CuGeO3 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∼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 Tg∼4.5 K. The dynamic relaxation rate λd is appreciably higher around Tg than below 4 K, and the correlation time τc of the magnetic fluctuations of 3d Cu moments in Cu0.96Zn0.04GeO3 is estimated to be τc∼10-8 s at 5 K