V51NMR study of the kagome staircase compoundNi3V2O8

We used $^{51}\text{V}$ NMR to study magnetic ordering in the ${\text{Ni}}_{3}{\text{V}}_{2}{\text{O}}_{8}$ single crystal with a Kagome staircase structure of Ni atoms. The NMR spectra were measured in the temperature range $T=(3--300)\text{ }\text{K}$ and magnetic fields $H=(2--9.4)\text{ }\text{T}$ directed along the main $\mathbit{a},\mathbit{b},\mathbit{c}$ axes of the orthorhombic $(Cmca)$ crystal. The local magnetic field at the $^{51}\text{V}$ NMR probe determines position and the shape of the corresponding NMR line. These parameters yield an unique information, respectively, on the uniform and the staggered spin components of the ordered Ni. The NMR data collected at $H\ensuremath{\ge}2\text{ }\text{T}$ are considered in line with predictions of the representation theory [A. Harris, Phys. Rev. B 76, 054447 (2007)] with a result that incommensurate amplitude-modulated structure of the spine ${\text{Ni}}_{\text{s}}$ spins acquires in the high-temperature incommensurate (HTI) phase two prominent nearly equal spin components ${S}_{a}\ensuremath{\approx}{S}_{c}⪢{S}_{b}$ instead of the longitudinal incommensurate spin-density wave (SDW) order with ${S}_{a}⪢{S}_{c},{S}_{b}$ as it was deduced from neutron-diffraction data [M. Kenzelmann et al., Phys. Rev. B 74, 014429 (2006)]. No noticeable variation of SDW polarization in the $\mathbit{ab}$ plane was detected below the HTI-low-temperature incommensurate (LTI) transition. In both the HTI and LTI phases two almost equal spin components of the ${\text{Ni}}_{\text{s}}$ spins ${S}_{a}\ensuremath{\approx}{S}_{c}⪢{S}_{b}$ exist at $Hl4.7\text{ }\text{T}$. Their phasing is still not determined. The bulk magnetization in these phases is explained by contribution of the cross-tie ${\text{Ni}}_{\text{c}}$ spins which antiferromagnetic structure in the LTI phase is canted along $H$.