MAGNETIC PHASE-DIAGRAM OF THE SPIN-PEIERLS CUPRATE CUGEO3

The magnetization of the spin-Peierls cuprate CuGeO3 was measured in magnetic fields up to 25 T at constant temperatures from 3.5 to 20.3 K. The transition temperature without the field is 14.0 K. The characteristic nonlinearity of the magnetization was observed below 13.4 K, which means the transition was from a dimerized phase to other phases. This transition is of first and second order below and above 10.0 K, respectively. The critical field of the transition between dimerized and magnetic phases is 12-13 T. The magnetic phase diagram of CuGeO3 agrees qualitatively with both experimental results of typical organic spin-Peierls materials and a theoretical calculation.