FeGaB Alloys for Magnetoelastic Coupling at Microwave Frequencies

Magnetoelastic coupling is important for many magnetoelectric applications such as devices based on surface acoustic waves. Fe₈₀Ga₂₀ is a high-performance magnetoelastic material due to its strong magnetoelastic response in the disordered A2 phase. In this work, we explored amorphous phases by adding boron into magnetron sputtered Fe₈₀Ga₂₀ films. Fe₈₀Ga₂₀ thin films with boron concentration from 2% to 16% were synthesized by co-sputtering from three targets and the compositions were characterized with X-ray photoemission spectroscopy. Structural characterization by X-ray diffraction indicated the structure of the films transitioning from crystalline to amorphous around 10% boron content. The coercivity, obtained from magnetization hysteresis loops, decreased rapidly from 75 Oe with 2% B to 4 Oe with 16% B, with the most rapid decrease right around the 10% B structure transition region. In addition to high magnetostriction, low damping is also desired to minimize energy loss in magnetic system. Using ferromagnetic resonance, we determine a low damping around 3×10^-3 in B-doped FeGa films. The magnetostriction constant of the B doped FeGa films was also characterized by measuring cantilever deflection in a rotating magnetic field.