  We explore a thermal mechanism of changing the anisotropy by femtosecond
laser pulses in dielectric ferrimagnetic garnets by taking a low symmetry
(YBiPrLu)3(FeGa)5O12 film grown on the (210)-oriented Gd3Ga5O12 substrate as a
model media. We demonstrate by means of spectral magneto-optical pump-probe
technique and phenomenological analysis, that the magnetization precession in
such a film is triggered by laser-induced changes of the growth-induced
magnetic anisotropy along with the well-known ultrafast inverse Faraday effect.
The change of magnetic anisotropy is mediated by the lattice heating induced by
laser pulses of arbitrary polarization on a picosecond time scale. We show that
the orientation of the external magnetic field with respect to the
magnetization easy plane noticeably affects the precession excited via the
anisotropy change. Importantly, the relative contributions from the ultrafast
inverse Faraday effect and the change of different growth-induced anisotropy
parameters can be controlled by varying the applied magnetic field strength and
direction. As a result, the amplitude and the initial phase of the excited
magnetization precession can be gradually tuned.
