Ferromagnetic resonance properties of multilayered (Fe ₈₀ Ga ₂₀ /B) _<i>n</i> thin films grown on LiNbO ₃ substrates

Acoustically driven ferromagnetic resonance (FMR) in magnetostrictive-piezoelectric thin-film heterostructures holds significant potential for detecting weak biomagnetic signals from human physiological activity. Minimizing the FMR linewidth is crucial for such applications. This study explores FMR linewidth reduction by examining the properties of alternately sputtered multilayered magnetostrictive $(\mathrm{Fe}\mathrm{Ga}/\mathrm{B}{)}_{n}$ thin films on piezoelectric ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_{3}$ substrates, all with 20 nm thicknesses. As the number of repeating layers (n) increases from 4 to 20, the damping constant declines sharply for n = 4--8, followed by a much slower decrease for n = 8--20. In contrast, inhomogeneity line broadening exhibits a U-shaped trend. These effects collectively yield minimal FMR linewidths at n = 12 and n = 16, demonstrating that optimizing n can effectively reduce the FMR linewidth. Notably, the lowest linewidths observed are smaller than those of a cosputtered $\mathrm{Fe}\mathrm{Ga}\mathrm{B}$ film with the same composition and thickness on an identical ${\mathrm{Li}\mathrm{Nb}\mathrm{O}}_{3}$ substrate. This suggests that the multilayered approach outperforms the conventional cosputtering approach for producing low-linewidth magnetic thin films, offering insights into acoustically driven FMR-based high-sensitivity magnetic field sensing devices.