$^{\mathrm{11}}$B Pulsed NMR Study of DyNi$_{\mathrm{2}}$B$_{\mathrm{2}}$C Single Crystals

DyNi$_{\mathrm{2}}$B$_{\mathrm{2}}$C is the only compound in the $R$Ni$_{\mathrm{2}}$B$_{\mathrm{2}}$C ($R =$ rare-earth) series where superconductivity at $T_{c} $\textasciitilde 6.2 K coexists with the antiferromagnetic ordering below the Nèel temperature$ T_{N}$ \textasciitilde 10.3 K. $^{\mathrm{11}}$B pulsed NMR measurements were performed at 8.0056 T to investigate the local electronic structures and \textit{4f} spin dynamics of DyNi$_{\mathrm{2}}$B$_{\mathrm{2}}$C powders and single crystals. The spectrum for the single crystal showed three narrow resonance peaks at 295 K due to the nuclear Zeeman splitting of a nuclear spin $I =$ 3/2 with quadrupolar perturbation. The $^{\mathrm{11}}$B NMR Knight shift of the single crystal was very large and highly anisotropic at $K=-$0.60{\%} and $+$0.27{\%} for the fields parallel and perpendicular, respectively, to the $c$-axis at 295 K. Considering the anisotropy of the Knight shift, we were able to simulate the $^{\mathrm{11}}$B NMR power pattern that agreed well with the measured spectrum. The linewidth was also large and anisotropic, and the linewidth value increased rapidly at low temperatures. The $^{\mathrm{11}}$B NMR shift and linewidth were found to be proportional to the magnetic susceptibility, indicating that the hyperfine field at the B site originates from the 4$f$ spins of Dy. Above $T_{N}$, the values for 1/$T_{\mathrm{1}}$ and 1/$T_{\mathrm{2}}$ were very large, showing slight increases at low temperatures. Below $T_{N}$, the values of 1/$T_{\mathrm{1}}$ and 1/$T_{\mathrm{2}}$ were suppressed significantly because of the slowing of the 4$f $spin fluctuation. This confirmed the huge change in Dy \textit{4f} spin dynamics across the antiferromagnetic transition.