Investigation of magnetic dipole-dipole interaction using magnetic density on solid oxygen based on first-principles approach

We have developed the computational method to estimate magnetic dipole-dipole interaction energy including magnetic spin density on three-dimensional materials, in the framework of density functional theory. We investigated the stable spin direction in oxygen molecule and α- and δ-phases of solid oxygen. Our method gave the result that the magnetic dipole-dipole interaction of realistic spin density distribution provides the stable magnetic moments perpendicular to the molecular axis, in contrary to the simple expectation from the isolated-spin moment model of the oxygen molecule. The reason has been explained by the spin density distribution of oxygen molecule and magnetic dipole field. Moreover, the result of magnetic anisotropy energy was found to be consistent with the experimental ones.