NMR study of magnetic structure and spin dynamics in $\alpha$-CoV$2$O$6$

CoV2O6, possessing the linear chain array of Co2+ ions in the crystal structure, has attracted much attention, since it shows the 1/3 magnetic plateau in the magnetization curve along c-axis. Its monoclinic form $\alpha$-CoV2O6 shows the antiferromagnetic (AFM) transition at the Neel temperature of 14 K in zero magnetic field (H = 0 T). Regarding the ferromagnetic (FIM) state in 1.5 T < H < 3.5 T, associated with the 1/3 magnetic plateau, several models have been previously proposed for its magnetic structure. But, they are not completely in accordance with each other.
In order to clarify the magnetic structures and spin dynamics of these magnetically ordered states, the measurements of V-NMR spectrum have been performed for the aligned powder sample of $\alpha$-CoV2O6. In the AFM state, it has been shown that the magnitude of the internal field at V site is 0.85 T and its direction is perpendicular to c-axis from the V-NMR spectra. In the FIM state, the V-NMR spectra indicate three V sites experiencing different magnetic field magnitudes. These internal fields could be explained by accounting for the dipole and the transfer field from Co spins with the up-up-down type structure of the FIM state. The anisotropy of the nuclear spin-lattice relaxation rate in these ordered states reinforces the argument.