Magnetic frustration induced formation of the spin-Peierls phase in CuGeO3: Experimental evidence

Measurements of the magnetostriction of single crystalline CuGeO3 at temperatures between 2 and 60 K and for magnetic fields up to 14 T are presented. At low temperatures the magnetostriction is dominated by changes of the spontaneous strains at the phase transitions characteristic for spin-Peierls systems. At higher temperatures a magnetoelastic coupling is found which is unexpectedly large and strongly anisotropic. A comparison of the magnetostriction well above the spin-Peierls transition temperature Tsp and the thermal expansion anomalies at Tsp yields a striking correlation between the uniaxial pressure dependencies of the spin-susceptibility and T-SP It is argued that this strongly supports electronic models of the spin-Peierls transition in CuGeO3 which are based on competing antiferromagnetic intrachain interactions.