ANOMALOUS SPECTRUM OF CS-133 NMR IN CSCUCL3 AROUND THE APPLIED FIELD-11-T

Cs-133 NMR experiment has been performed on CsCuCl3 at 4.2 K under the applied magnetic field parallel to the crystal c-axis. An anomalous spectrum has been observed at the critical field of 11.19 T, where the magnetization j ump was detected previously. At the critical field, the spectrum is abruptly cut off with no hysteresis for the sweep direction of the magnetic field. The critical field is independent of the operating frequency of the NMR experiment. The result can be explained by the theoretical model of the field-induced transition due to the quantum spin fluctuation in the one-dimensional ferromagnet with S=1/2.