SPIN DYNAMICS IN CUGEO3 STUDIED BY MUON SPIN ROTATION

We report a muon spin rotation (mu SR) study of the magnetic properties of the Cu2+ quasi-one-dimensional CuGeO3 system and its lightly-doped derivative Cu0.97Zn0.03GeO3. Susceptibility measurements on CuGeO, show a sudden change in the vicinity of 14 K that has been interpreted before as a magnetic transition to a spin-Peierls state. mu SR shows no evidence of spin freezing below 14 K, implying that the transition is to a magnetic state with no static (random or ordered) electronic moments. A modest slowing down of the electronic spin dynamics is also identified at this temperature. Similarly, no evidence of a transition to a static magnetic state is found for Cu0.97Zn0.03GeO3 whose susceptibility shows hysteretic behaviour between zero-field and field cooled measurements at 4 K, previously ascribed to spin-glass-like behaviour. Given the nature of the muon spin as a local magnetic probe, the present results necessitate a re-interpretation of the origin of the susceptibility anomaly observed in the doped system.