Nature Commun. 6, 6724 (2015)

Modifying the magnetization of materials by means of ultrashort laser pulses has proved to be faster, by several orders of magnitude, than other approaches based on the application of magnetic fields or spin-polarized current pulses. Although laser excitations typically produce an attenuation of the magnetization due to heating, in some materials they can cause transitory enhancements owing to strong coupling among spin, charge, and orbital angular moment. Masakazu Matsubara and colleagues now demonstrate that the magnetization can be increased or decreased in materials with a low density of carriers in the conduction band and with a high density of magnetic moments, by controlling the density of resonantly photoexcited carriers. Using this approach, they show changes of 10% in the magnetization strength within 3 ps in low-doped Eu1−xGdxO. Besides providing insights into the non-equilibrium photoinduced magnetization dynamics, this result may constitute a step towards ultrafast optically controlled ferromagnetic devices.