  Ultrafast optical excitation of gold-cobalt bilayers triggers the nontrivial
interplay between the electronic, acoustic, and magnetic degrees of freedom.
Laser-heated electrons generated at the gold-air interface diffuse through the
layer of gold and strongly overheat the lattice in cobalt resulting in the
emission of ultrashort acoustic pulses and generation of exchange-coupled
magnons. Time-resolved optical measurements allow for extracting the thermal
boundary (Kapitza) resistances at metal/metal interfaces and the hot electron
diffusion length in ferromagnetic materials. Both the experimental data and the
analytical treatment of the two-temperature model reveal the role of the
Kapitza resistance in transient lattice overheating.
