  Nanoscale heterostructure design can control laser-induced heat dissipation
and strain propagation as well as their efficiency for driving magnetization
precession. We use insulating MgO layers incorporated into metallic Pt-Cu-Ni
heterostructures to block the propagation of hot electrons. Ultrafast x-ray
diffraction (UXRD) experiments quantify how this enables controlling the
spatio-temporal shape of the transient heat and strain, which drive the
magnetization dynamics in the Ni layer. The frequency of the magnetization
precession observed by the time-resolved magneto-optical Kerr effect (MOKE) in
polar geometry is systematically tuned by the magnetic field orientation. The
combined experimental analysis (UXRD and MOKE) and modeling of transient
strain, heat and magnetization uniquely highlights the importance of
quasi-static strain as a driver of precession, when the magnetic material is
rapidly heated via electrons. The concomitant effective field change
originating from demagnetization partially compensates the change induced by
quasi-static strain. Tailored strain pulses shaped via the nanoscale
heterostructure design provide an equally efficient, phase-matched driver of
precession, paving the way for opto-magneto-acoustic devices with low heat
energy deposited in the magnetic layer.
