Ultrafast strain excitation in highly magnetostrictive terfenol: Experiments and theory

Abstract

We experimentally and analytically investigate laser excitation of picosecond longitudinal and shear acoustic pulses in highly magnetostrictive terfenol-${\mathrm{TbFe}}_{2}$-epitaxial thin films. We report a magnetoelastic mechanism for picosecond longitudinal and shear acoustic strain excitation, so-called direct transient demagnetostriction, which denotes the ultrafast laser-induced demagnetization and release of static magnetostrictive built-in strains. From analytical considerations and numerical modeling, we demonstrate that the efficiency of ultrashort longitudinal and shear acoustic strains generation strongly depends on the magnetization orientation with respect to the lattice crystallographic directions. Overall, our study provides insight into ultrafast acoustic waves excitation and detection in all sorts of magnetic materials from laser-based mechanisms.