Evidence of Magnon-Mediated Orbital Magnetism in a Quasi-2D Topological Magnon Insulator.

We explore spin dynamics in Cu(1,3-bdc), a quasi-2D topological magnon insulator. The results show that the thermal evolution of the Landé factor () is anisotropic: decreases while increases with increasing temperature . Moreover, the anisotropy of the factor (Δ) and the anisotropy of saturation magnetization (Δ) are correlated below 4 K, but they diverge above 4 K. We show that the electronic orbital moment contributes to the anisotropy at lower , while the topological orbital moment induced by thermally excited spin chirality dictates the anisotropy at higher . Our work suggests an interplay among topology, spin chirality, and orbital magnetism in Cu(1,3-bdc).