We present the results of the magnetization and dielectric constant measurements on untwinned single crystal samples of the frustrated S=1/2 chain cuprate LiCu_2O_2. Novel magnetic phase transitions were observed. A spin flop transition of the spiral spin plane was observed for the field orientations H||a,b. The second magnetic transition was observed at H~15 T for all three principal field directions. This high field magnetic phase is discussed as a collinear spin-modulated phase which is expected for an S=1/2 nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic chain system.
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