Ultrafast optical probe of coherent acoustic phonons in ${Co}_{2}MnAl$ Heusler film

In this work, pronounced oscillations in the time-resolved reflectivity of Heusler alloy Co₂MnAl films which are epitaxially grown on GaAs substrates are observed and investigated as a function of film thickness, probe wavelength, external magnetic field and temperature. Our results suggest that the oscillation response at 24.5 GHz results from the coherent phonon generation in Co₂MnAl film and can be explained by a propagating strain pulse model. From the probe wavelength dependent oscillation frequency, a sound velocity of (3.85 ± 0.1)×10³ m/s at 800 nm for the epitaxial Co₂MnAl film is determined at room temperature. The detected coherent acoustic phonon generation in Co₂MnAl reported in this work provides a valuable reference for exploring the high-speed magnetization manipulation via magnetoelastic coupling for future spintronic devices based on Heusler alloy films. (paper)