Effect of Bi/In co-doing on the Gilbert damping and Faraday rotation of Tm₃Fe₅O₁₂ film

Rare-earth iron garnet materials are applied extensively in magnetic devices and magneto-optical isolators owing to their superior properties. This Letter presents a detailed investigation of the Gilbert damping and Faraday rotation of Bi/In-doped Tm₃Fe₅O₁₂ (Bi/In:TmIG) films on SGGG (111) substrates. An increase in indium doping concentration caused the saturation magnetization to rise, and the coercive force decreased along the in-plane magnetization direction. This was accompanied by concurrent variations in the Faraday rotation angle and temperature coefficient. The Gilbert damping factor and ferromagnetic resonance linewidth of the BiTmIn_0.5IG sample dropped to 7.51 × 10⁻³ and 16 Oe at 3 GHz, respectively. In³⁺ doping affects the crystal structure and magnetic properties of Bi-doped TmIG, in addition to the coupling interactions between Fe³⁺ ions at the a- and d-sites, respectively. The low damping factor with narrow resonance linewidth has promising potential for the further application of TmIG in magnetron devices and magneto-optical devices.