  The multiferroic compound CuO exhibits low temperature magnetic properties
similar to antiferromagnetic iron oxides, while the electronic properties have
much more in common with the high $T_c$ cuprate superconductors. This suggests
novel possibilities for the ultrafast optical excitation of magnetism. On the
basis on atomistic spin dynamics simulations, we study the effect of
phonon-assisted multimagnon absorption and photodoping on the spin dynamics in
the vicinity of the first-order phase transition from collinear to spin-spiral
magnetic order. Similar as in recent experiments, we find that for both
excitations the phase transition can proceed on the picosecond timescale.
Interestingly, however, these excitation mechanisms display very distinct
dynamics. Following photodoping, the spin system first cools down on sub-ps
timescales, which we explain as an ultrafast magnetocaloric effect. Opposed to
this, following phonon-assisted multimagnon excitation the spin systems rapidly
heats up and subsequently evolves to the noncollinear phase even under the
influence of isotropic exchange interactions alone.
