[21a-P02-1~50] 10 Spintronics and Magnetics(Poster)

▲ [21a-P02-26] Role of magnetocrystalline anisotropy and magnetic dipole-dipole interaction in spin Seebeck effect at NiO/Pt

〇(M2)Andi Gumarilang Ahmadi¹, Kenji Nawa¹, Kohji Nakamura¹ (1.Mie Univ.)

Keywords:magnon, magnetocrystalline anisotropy, magnetic dipole-dipole interaction

Propagation of collective spin deviation in magnetic materials, known as spin-wave or magnon, is determined by its magnetic anisotropy, which generates spin-current under a thermal gradient, so-called spin Seebeck effect (SSE). In an antiferromagnetic insulator NiO, the magnetic anisotropy originates from magnetic dipole-dipole interaction (MDI) and magnetocrystalline anisotropy (MCA). In the present work, we theoretically demonstrated magnon transport and spin Seebeck effect at NiO/Pt using the second quantization method combined with first-principles calculations and discussed the role of MDI and MCA. We found that the dominant anisotropy in NiO arises from MDI, which lifts the degeneracy of spin-wave modes (α-mode and β-mode) and creates spin-current through SSE without an applied external field. A significant energy shift of the higher frequency α-mode was observed due to MDI compared to that in the lower frequency β-mode. In contrast, the shift and gap opening due to MCA is much weaker by three orders of magnitude. MDI creates a velocity difference between the two modes at the long-wavelength limit while propagating with nearly identical velocities at the short-wavelength. Using magnon diffusion theory, we found that the MDI simultaneously increases the magnitude of spin-current due to magnon drift in the bulk region and magnon accumulation at the interface between NiO/Pt, whereas the total spin-current pumped into Pt decreases as the MDI strength increases. However, the spin-current generated by the interfacial magnon accumulation has a negative sign in contrast to that of magnon drift in the bulk, which implies magnon accumulation contributes to slowing the spin-current pumped into the adjacent metal. Therefore, the decrease of the total spin-current pumped is ascribed to the magnon accumulation at the interface.