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 -TbFe2 -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.

Concepts and use cases for picosecond ultrasonics with x-rays

“…However, the modeled strain map does not only help to rationalize the strain observed in a PUX experiment but can furthermore guide and support the interpretation of strain signatures in all-optical data, e.g. from time-resolved magneto-optics and reflectivity [15] , [36] , [114] .

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Concepts and use cases for picosecond ultrasonics with x-rays

“…However, the modeled strain map does not only help to rationalize the strain observed in a PUX experiment but can furthermore guide and support the interpretation of strain signatures in all-optical data, e.g. from time-resolved magneto-optics and reflectivity [15,36,111].…”

Ultrafast magnetoacoustics in Galfenol nanostructures

“…Subsequent experiments with Ni films demonstrated the excitation of coherent magnons by coherent phonons generated directly in a ferromagnetic material [13] . This work defined a new research field, which was developed experimentally [14] , [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] and theoretically [26] , [27] , [28] , [29] , [30] , [31] , [32] , [33] , [34] , [35] over the next decade.…”

“…The range of materials studied by ultrafast magnetoacoustic experiments is not so wide. It includes the well-studied Ni [13] , [16] , [17] , [18] , [25] , Yttrium-Iron Garnets (YIG) [19] , [20] , [21] , alloys like (Ga,Mn)As [10] , [11] and Terfenol-D [23] , and multilayer structures [22] . The present review focuses on ultrafast magnetoacoustic experiments with epitaxial films of the metallic ferromagnetic alloy of Iron and Gallium known as Galfenol [49] .…”