学术文献库

Temperature and field dependence of collective spin excitations or magnon in monolayer honeycomb spin lattices is investigated using an anisotropic exchange XZ-Heisenberg model in an external field. Magnetic phase transition in the presence of the transverse field is the spin reorientation (SR) transition with magnon intensity existing above the SR temperature. The transverse field either decreases or sustains the spin-wave intensity in the temperature region below or above the SR temperature, respectively. The gap of the zero-momentum low-energy magnon branch closes at the SR transverse field, which is the critical quantum phase transition field at zero temperature. The application of the model to a two-dimensional CrI$_3$ explains the existence of the zero-momentum magnon mode above the Curie temperature and shows the suitable values of the exchange parameters compared with the DFT calculations. The estimated magnon velocity near the Dirac point in this material is about 1.74 km/s.