Magnetostriction and Temperature Dependent Magnetic Damping in Boron Doped Fe₈₀Ga₂₀ Thin Films.

Owing to its short wavelength and long propagation distance, surface acoustic wave is a promising candidate for miniaturizing microwave devices such as isolators and circulators, which rely on large nonreciprocity and low propagation loss facilitated by low damping and large magnetoelastic coupling. Fe₈₀Ga₂₀ is a popular choice for the magnetoelastic layer due to its high magnetoelastic response. Here, we investigated the effects of boron doping concentration on magnetostriction and temperature dependent Gilbert damping in magnetron sputtered (Fe₈₀Ga₂₀)_1-xB_x films. Structural characterization by X-ray diffraction (XRD) revealed a reduction in Fe (100) peak when increasing B from 2% to 8%, and vanishing of the peak at 10% B, indicating gradually stabilized disorder. Magnetic hysteresis loops showed a decrease in coercivity from 76 Oe to 3 Oe while incorporating more B, consistent with structural change observed in XRD. We identified 10% as the optimal doping concentration for generating both large magnetostriction of 50 ppm and low Gilbert damping of 6×10^-3. The temperature dependence of the damping showed an increase at low temperatures with a peak around 40 K and we associate the relative increase Δα/α_RT, which has a maximum of 55.7% at 8% boron, with magnetoelastic contributions to the damping.