Magnetic interactions and the pressure phase diagram of CuGeO3

A pressure and temperature dependent Raman study of the vibrational and spin dynamics in CuGeO3 is presented. A new, low temperature, high pressure phase has been identified, and a pressure temperature phase diagram is proposed for CuGeO3. The pressure dependence of the effective exchange interaction, of the spin-Peierls gap and of the spin-Peierls temperature, strongly supports a model in which next-nearest-neighbor interactions stabilize the spin-Peierls ground state. The Raman-data allow for a quantitative estimate of the pressure dependence of the next-nearest-neighbor interactions.