Role of Magnetic Dipole-Dipole Interaction on Magnon Properties in Nio

Magnetic anisotropy in materials, such as magnetocrystalline anisotropy (MCA) and magnetic dipole-dipole interaction anisotropy (MDIA), plays roles in propagation of magnon. Here, we show theoretically that the MDIA in Nickel Oxide (NiO) substantially lifts the degeneracy between magnon frequencies of α and β modes. A significant shift of the magnon frequency in the α mode to higher frequency is observed, while the β mode is weakly affected. By using the magnon dispersion relation and magnon coherent states, the frequency shift is found to be semi-classically explained by the ellipticity and the MDIA. Additionally, the MDIA determines a difference in the magnon group velocities that contribute to spin transport phenomena.