Complex Field-Induced States in Linarite PbCuSO sub(4)(OH) sub(2) with a Variety of High-Order Exotic Spin-Density Wave States

Low-temperature neutron diffraction and NMR studies of field-induced phases in linarite are presented for magnetic fields H || b axis. A two-step spin-flop transition is observed, as well as a transition transforming a helical magnetic ground state into an unusual magnetic phase with sine-wave-modulated moments ||H. An effective J sub(1) super(~)-J sub(2 ) super(~) single-chain model with a magnetization-dependent frustration ratio alpha sub(eff) = J sub(2)/J sub(1) is proposed. The latter is governed by skew interchain couplings and shifted to the vicinity of the ferromagnetic critical point. It explains qualitatively the observation of a rich variety of exotic longitudinal collinear spin-density wave, SDW sub(p), states (9 > or = p > or = 2).