  Dynamical strain generated upon excitation of a metallic film by a
femtosecond laser pulse may become a versatile tool enabling control of
magnetic state of thin films and nanostructures via inverse magnetostriction on
a picosecond time scale. Here we explore two alternative approaches to
manipulate magnetocrystalline anisotropy and excite magnetization precession in
a low-symmetry film of a magnetic metallic alloy galfenol (Fe,Ga) either by
injecting picosecond strain pulse into it from a substrate or by generating
dynamical strain of complex temporal profile in the film directly. In the
former case we realize ultrafast excitation of magnetization dynamics solely by
strain pulses. In the latter case optically-generated strain emerged abruptly
in the film modifies its magnetocrystalline anisotropy, competing with
heat-induced change of anisotropy parameters. We demonstrate that the
optically-generated strain remains efficient for launching magnetization
precession, when the heat-induced changes of anisotropy parameters do not
trigger the precession anymore. We emphasize that in both approaches the
ultrafast change of magnetic anisotropy mediating the precession excitation
relies on mixed, compressive and shear, character of the dynamical strain,
which emerges due to low-symmetry of the metallic film under study.
