Spin density wave in insulating ferromagnetic frustrated chain LiCuVO

Masuda, Takatsugu*; Hagihara, Masato*   ; Kondo, Yosuke*; Kaneko, Koji   ; Metoki, Naoto   

We study a field-induced quantum phase in the weakly-coupled ferromagnetic frustrated chain LiCuVO by a neutron diffraction technique. A new incommensurate magnetic peak is observed at H 8.5 T. The field-dependent propagation vector is identified with the spin density wave correlation in the theoretically predicted magnetic quadrupole order. Quantum fluctuation, geometrical frustration, and interchain interaction induce an exotic spin density wave long-range order in the insulating magnet.