Experimental evidence for a spin-Peierls-transition in α' -NaV2O5

We present the first measurements of magnetisation and Raman light scattering on α'- NaV 2 O 5 single crystals. Below 34 K, we observe a pronounced isotropic decrease of the susceptibility indicating the opening of a spin gap. The transition temperature is slightly field dependent. Raman experiments reveal a crystallographic distortion at the transition. Our results clearly establish α'-NaV 2 O 5 to be the second inorganic spin-Peierls system.