Ultralow Damping in Epitaxial Spinel Ferrite Thin Films

Magnetic insulator thin films are expected to be excellent media for spin-based information without charge flow. This expectation relies on the premise that magnetic insulators exhibit lower magnetic damping compared to their metallic counterparts. However, insulating behavior is not a sufficient requirement for low damping, as evidenced by the very limited options for low-damping magnetic insulators. In this presentation, we demonstrate a new class of ultralow-damping insulator based on design criteria minimizing orbital angular momentum as well as crystalline and cation valence disorder. Specifically, we show ultralow damping in spinel structure magnesium aluminum ferrite (MAFO), in which magnetization arises solely from Fe³⁺ ions with zero orbital angular momentum. Epitaxial MAFO films with thicknesses <20 nm exhibit ferromagnetic resonance linewidths of ≈0.6 mT around 10 GHz and Gilbert damping parameters of ≈0.0015. Our findings demonstrate that minimal spin-orbit coupling and coherent epitaxy allow for ultralow damping in ferrite thin films, expanding the materials choices for energy-efficient insulator spintronics.