Field-tunable acoustic damping in FeGaB/AlScN shear-mode solidly mounted resonators

We theoretically investigate field-tunable acoustic damping in a FeGaB/tilted-AlScN/Mo thickness-shear solidly mounted resonator (SMR) using a coupled transfer-matrix and Landau–Lifshitz–Gilbert (TMM-LLG) model. The field- and frequency-dependent complex elastic stiffness of FeGaB is incorporated into the multilayer transfer matrix to calculate electrical impedance, series quality factor Qs, and effective electromechanical coupling keff2. A three-pair Mo/SiO2 Bragg reflector confines acoustic energy, while a 15° c-axis-tilted AlScN layer excites a pronounced shear mode near 1.69 GHz. Under perpendicular DC magnetic bias, acoustically driven ferromagnetic resonance (ADFMR) enables resonant phonon–magnon energy transfer and strongly reduces Qs. The resulting Q-factor modulation yields a maximum calculated sensitivity SQ ≈ 1400 T−1 at Ha ≈ 0.13 T and an estimated limit of detection (LoD) of 71.4 μT for ΔQmin = 0.1. Despite strong magneto–acoustic attenuation, keff2 remains above 3.69%, indicating sustained piezoelectric transduction. The contribution of this work is the device-level implementation of ADFMR-induced Qs modulation in a thickness-shear SMR, rather than a new magneto–acoustic mechanism. The required static bias is an external system-level requirement. The LoD is model-based and should not be interpreted as an experimentally validated noise floor or state-of-the-art detection limit.