Large Interband-Driven Anisotropic Gilbert Damping of a Few Atomic Layers of Fe in Contact with MgO

Magnetization control in spintronic devices is governed by the Gilbert damping constant, which describes the energy dissipation in magnetization dynamics. Although Gilbert damping is often treated as an isotropic scalar, crystalline symmetry can induce orientational damping anisotropy. This anisotropy is commonly attributed to intraband scattering associated with changes in the electronic density of states, whereas interband scattering has generally been assumed to be isotropic. Here, we show that the anisotropic Gilbert damping of a few atomic layers of Fe in contact with MgO is governed by interband scattering. Time-resolved magneto-optical Kerr measurements reveal that intrinsic damping increases by nearly a factor of 3 when the magnetization tilts from in-plane to out-of-plane. Combined strain-dependent experiments and first-principles calculations identify interband scattering at the Fe/MgO interface as the origin of this effect, providing new insights into magnetization dynamics beyond the conventional intraband-dominated picture.