Surface-Acoustic-Wave Induced Ferromagnetic Resonance in Fe Thin Films and Magnetic Field Sensing

Resonant magnetoelastic coupling (MEC) is demonstrated in an Fe thin film epitaxially grown on a piezoelectric GaAs substrate with application of subgigahertz surface acoustic waves (SAWs). The frequency at which resonant MEC is achieved is reduced far below 1 GHz by the application of a small in-plane magnetic field. Moreover, the resonance, observable by attenuation and velocity changes of the SAW, can be switched on and off by a small (0.1 oC) angular rotation of this in-plane field. This angular sensitivity makes SAW-ferromagnet devices attractive for sensing applications, such as wireless, battery-free, and interrogable magnetic-field monitors. Using a simple magnetization dynamics model that takes into account the Fe magnetic anisotropy and the softening of the magnetic precession modes, we are able to describe the observed salient features.