11:00 〜 12:40
▲ [22a-P09-10] Magnon transport in NiO based on first-principles calculations
キーワード：Magnon Transport, NiO, Spin Seebeck Effect
Nickel Oxide (NiO) is an antiferromagnetic insulator that exhibits spin-current when thermal gradient is applied. This phenomenon is called spin Seebeck effect (SSE) and originated from two thermally excited spin wave or magnon modes that carry spin current in the opposite directions. Here, we have developed a method for magnon transport by combining first-principles calculations and spin Hamiltonian in second quantization and then extended this to treat the magnon transport including SSE using Boltzmann transport and diffusion theory. Full-potential Linearized Augmented Plane Wave (FLAPW) method with Generalized Gradient Approximation (GGA) and Hubbard correction (Ueff) are employed to calculate the parameters needed for spin Hamiltonian model that consists of spin-exchange and magnetization anisotropy terms. We first confirmed that Ueff value between 5 eV and 7.5 eV gives the spin magnetic moments, spin-exchange, and anisotropy constants that roughly agree with experiment results, but the band gap (~3.4 eV) is slightly underestimated to that in experiments. As the Ueff value increases, the spin-exchange constant decreases, while the magnetization anisotropy term has increasing trends. This follows from the density of states which shows high Ueff value pushes down the valence d-orbital states to lower energy levels, reducing the overlap between wavefunctions and enhancing spin-orbit coupling in Ni atoms. Moreover, high Ueff value gives almost flat magnon dispersion curve. From the fact that magnon velocity equals to gradient of dispersion curve, this implies that the corresponding spin current is very small for high Ueff.