Persistent spin dynamics intrinsic to amplitude-modulated long-range   magnetic order
  An incommensurate elliptical helical magnetic structure in the frustrated coupled-spin-chain system FeTe2O5Br is surprisingly found to persist down to 53(3) mK (T/T_N ~ 1/200), according to neutron scattering and muon spin relaxation. In this state, finite spin fluctuations at T -> 0 are evidenced by muon depolarization, which is in agreement with specific-heat data indicating the presence of both gapless and gapped excitations. We thus show that the amplitude-modulated magnetic order intrinsically accommodates contradictory persistent spin dynamics and long-range order and can serve as a model structure to investigate their coexistence. 
M. Pregelj, A. Zorko, O. Zaharko, D. Arcon, M. Komelj, A. D. Hillier   and H. Berger
cond-mat.str-el