MAGNETIC FRUSTRATION INDUCED FORMATION OF THE SPIN-PEIERLS PHASE IN CUGEO3 - EXPERIMENTAL-EVIDENCE

Measurements of the magnetostriction of single crystalline CuGeO3 at t emperatures between 2 and 60 K and for magnetic fields up to 14 T are presented. At low temperatures the magnetostriction is dominated by ch anges of the spontaneous strains at the phase transitions characterist ic for spin-Peierls systems. At higher temperatures a magnetoelastic c oupling is found which is unexpectedly large and strongly anisotropic. A comparison of the magnetostriction well above the spin-Peierls tran sition temperature Tsp and the thermal expansion anomalies at Tsp yiel ds a striking correlation between the uniaxial pressure dependencies o f the spin-susceptibility and T-SP It is argued that this strongly sup ports electronic models of the spin-Peierls transition in CuGeO3 which are based on competing antiferromagnetic intrachain interactions.