Magnetic phase diagram of the quantum spin chain compound SrCo₂V₂O₈: a single-crystal neutron diffraction study

We explore magnetic order in the quantum spin chain compound SrCo2V2O8 up to 14.9 T and down to 50 mK, using single-crystal neutron diffraction. Upon cooling in zero-field, commensurate antiferromagnetic (C-AFM) order with modulation vector kC = (0, 0, 1) develops belowTN ; 5.0 K. Applying an external magnetic field (HPc axis) destabilizes this C-AFM order, leading to an order-disorder transition betweenTN and∼1.5 K. Below 1.5 K, a commensurate to incommensurate (IC-AFM)transition occurs at 3.9 T, above which the magnetic reflections can be indexed by kIC = (0, 0, 1 ± δl). The incommensurability δlscales monotonically withHuntil the IC-AFM order disappears around 7.0 T.Magnetic reflections modulated by kC emerge again at higher fields.While the characters of the C-AFM, IC-AFM and the emergent AFM order in SrCo2V2O8 appear to fit the descriptions of the Néel, longitudinal spin density wave and transverse AFM order observed in the related compound BaCo2V2O8, our results also reveal several unique signatures that are not present in the latter, highlighting the inadequacy of mean-field theory in addressing the complex magnetic order in systems of this class.