Spin correlations in the S=1 armchair chain Ni2NbBO6 as seen from NMR*

We report our nuclear magnetic resonance (NMR) study on the structurally spin chain compound Ni2NbBO6 with complex magnetic coupling. The antiferromagnetic transition is monitored by the line splitting resulting from the staggered internal hyperfine field. The magnetic coupling configuration proposed by the first-principle density functional theory (DFT) is supported by NMR spectral analysis. For the spin dynamics, a prominent peak at T similar to 35 K well above the N eel temperature (T (N) similar to 20 K at mu (0) H = 10 T) is observed from the spin-lattice relaxation data. As compared with the dc-susceptibility, this behavior indicates an antiferromagnetic coupling with the typical energy scale of similar to 3 meV. Thus, the Ni2NbBO6 compound can be viewed as strongly ferromagnetically coupled armchair spin chains along the crystalline b-axis. These facts place strong constraints on the theoretical model for this compound.