MAGNETIC PHASE-DIAGRAM AND ANTIFERROMAGNETIC-RESONANCE IN CUGE1-YSIYO3

Magnetization and ESR measurements have been performed on Si-doped CuG e1-ySiyO3 (y = 0.01 and 0.02) single crystals. The y = 0.01 sample sho ws a spin-Peierls transition at T-sP = 11 K as well as undoped materia l and additionally show an antiferromagnetic state below T-N = 2.8 K. When an external field is applied to the c-axis below T-N, two magneti zation jumps due to the spin-flop and the transition from dimerized sp in-Peierls phase to magnetic phase are observed at 0.98 T and 11.5 T, respectively, which means the coexistence of spin-Peierls and antiferr omagnetic states. On the other hand, the y = 0.02 sample shows only an antiferromagnetic transition at T-N = 4.8 K.