Acoustically Driven Ferromagnetic Resonance in Diverse Ferromagnetic Thin Films

We report the first study of diverse ferromagnetic thin films via acoustically driven ferromagnetic resonance (ADFMR). Angle and field-dependent ADFMR was performed at room temperature on thin films of FeCo, FeCoGd, FeGaB, and FeCoSiB, which take the place of the ferromagnetic Ni film traditionally used in these experiments, with a few exceptions. Surface acoustic wave (SAW) devices are operated at three harmonics in the 0.8-2 GHz frequency range. Each magnetic material has a unique ADFMR signature: FeCo shows a standard 4-lobe pattern with a broad ~100 mT linewidth; FeCoGd breaks odd symmetry and reveals an additional low-field lobe; and FeGaB and FeCoSiB show extreme asymmetry and narrow linewidths. In FeCoSiB, we observe nonreciprocal SAW propagation. We also perform direct comparison of ADFMR and standard ferromagnetic resonance (FMR) on the same devices, revealing that ADFMR absorption is measurable even when FMR signals are extremely weak, and magnetic anisotropy does not fully explain asymmetry observed in ADFMR. These results demonstrate that strain-driven magnetization dynamics is a rich field; the effects can be observed in a variety of materials with unexpected behavior, motivating further work in the field.