Femtosecond laser excitation drives ferromagnetic gadolinium out of magnetic equilibrium

Phys Rev Lett. 2012 Aug 3;109(5):057401. doi: 10.1103/PhysRevLett.109.057401. Epub 2012 Jul 31.


The temporal evolution of the exchange-split Δ(2)-like Σ valence bands of the 4f-ferromagnet gadolinium after femtosecond laser excitation has been studied using angle-resolved photoelectron spectroscopy based on high-order harmonic generation. The ultrafast drop of the exchange splitting reflects the magnetic response seen in femtosecond magnetic dichroism experiments. However, while the minority valence band reacts immediately, the response of the majority counterpart is delayed by 1 picosecond and is only half as fast. These findings demonstrate that laser excitation drives the valence band structure out of magnetic equilibrium.