NMR study of the spin correlations in the $S=1$ armchair chain Ni$_2$NbBO$_6$

TL;DR

This study uses NMR to investigate the spin correlations and magnetic properties of Ni$_2$NbBO$_6$, revealing strong ferromagnetic coupling in armchair chains and supporting the magnetic structure proposed by DFT calculations.

Contribution

The paper provides the first NMR analysis of Ni$_2$NbBO$_6$, confirming its magnetic coupling configuration and characterizing its spin dynamics and antiferromagnetic transition.

Findings

Antiferromagnetic transition observed at 20 K via line splitting.

A prominent peak at 35 K indicates significant spin dynamics above T_N.

Strong ferromagnetic coupling along the b-axis in armchair chains.

Abstract

We report our nuclear magnetic resonance (NMR) study on the structurally spin chain compound Ni$_2$NbBO$_6$ 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 our NMR spectral analysis. For the spin dynamics, a prominent peak at $T\sim35$ K well above the N\'{e}el temperature ($T_N\sim20$ K at $\mu_0H=10$ T) is observed from the spin-lattice relaxation data. As compared with the dc-susceptibility, this behavior indicates a antiferromagnetic coupling with the typical energy scale of $\sim3$ meV. Thus, the Ni$_2$NbBO$_6$ compound can be viewed as strongly ferromagnetically coupled armchair spin chains along the crystalline $b$-axis. These facts place strong constraints to the theoretical model for this compound.