Electron spin resonance study on the 4f honeycomb quantum magnet YbCl3

The local magnetic properties of Yb${}^{3+}$ in the layered honeycomb material YbCl${}_3$ were investigated by electron spin resonance on single crystals. For in-plane and out-of-plane field orientations the $g$-factor shows a clear anisotropy ($g_{\mathrm{\parallel }}=2.97(8)$ and $g_{\mathrm{\perp }}=1.53(4)$), whereas the low temperature exchange coupling and the spin relaxation display a rather isotropic character. At elevated temperatures the contribution of the first excited crystal field level ($21\pm 2$~meV) dominates the spin relaxation.