Role of Magnetic Dipole-Dipole Interaction on Magnon in NiO

The role of magnetic anisotropy on magnon in NiO was theoretically investigated. By using first-principles calculations, magnetic parameters of spin-exchange constants, magnetocrystalline anisotropy (MCA) constant, and magnetic moment for the anisotropy by magnetic dipole -dipole interaction (MDIA) were extracted, where the MDIA is found to have a more dominant contribution to the magnetic anisotropy than the MCA does. Second quantization representation reveals that the MDIA lifts the degeneracy to two magnon modes, labeled as alpha and beta modes, and agrees with experiments. The magnon frequency in the a mode has a large shift to higher frequency due to the MDIA, while the beta mode is less affected, which is successfully illustrated by the different magnetization precessions of two-sublattices antiferromagnet. Finally, the MDIA creates magnon group velocity difference between the two modes at shorter wavevectors, which contributes to spin transport phenomena.