Muon spectroscopy investigation of anomalous dynamic magnetism in NiI\(_2\)

We present the results of muon-spin relaxation (\(\mu^{+}\)SR) measurements of the van der Waals magnet NiI\(_2\), which probe magnetic phase transitions at \(T_{\mathrm{N1}}=73\)K and \(T_{\mathrm{N2}}=60\)K. Supporting density functional theory (DFT) calculations allow the determination of a single muon stopping site whose magnetic environment is consistent with the proposed ground-state magnetic structure. \(\mu^{+}\)SR measurements of the dynamics reveal behavior consistent with spin-wave excitations below \(T_{\mathrm{N2}}\), with an additional contribution from a nonmagnetic component of the material. In the region \(T_{\mathrm{N1}}