Nature 496, 69–73 (2013)

Ultrafast all-optical switching of magnetism using coherent spin manipulation is one potential route for pushing today's magnetic memory and logic devices to terahertz switching speeds. However, demonstrations have so far been limited to the picosecond and nanosecond regimes. Now, by establishing a 'colossal' magnetization component from an antiferromagnetic ground state, Tianqi Li and co-workers from the USA and Greece have switched the antiferromagnetic ordering in Pr0.7Ca0.3MnO3 to ferromagnetic ordering on a timescale of 120 fs using a pump photoexcitation intensity of 5.8 mJ cm−2. They observed a huge temperature-dependent magnetization with a photoexcitation threshold behaviour, which they attribute to a non-equilibrium spin-exchange mechanism. Femtosecond-laser-excited coherence between electronic states can switch the magnetic order by abruptly destroying the delicate balance between competing phases of correlated materials.