Abstract Nature Physics: Coherent ultrafast magnetism induced by femtosecond laser pulses
The quest for ultrafast magnetic processes has triggered a new field of research—femtomagnetism: using femtosecond laser pulses to demagnetize ferromagnetic metallic thin films. Despite being the subject of intense research for over a decade, the underlying mechanisms that govern the demagnetization remain unclear. Here, we investigate how an ultrashort laser pulse couples to the spin of electrons in ferromagnetic metals. It is shown that a single 50-fs laser pulse couples efficiently to a ferromagnetic film during its own propagation. This result indicates that the material polarization induced by the photon field interacts coherently with the spins. The corresponding mechanism has its origin in relativistic quantum electrodynamics, beyond the spin–orbit interaction involving the ionic potential. In addition, this coherent interaction is clearly distinguished from the incoherent ultrafast demagnetization associated with the thermalization of the spins. We forecast that the corresponding coherent self-induced processes are the dawn of a new era for future research in magnetism.
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In a study published in the specialist journal Nature Physics, a team led by Jean-Yves Bigot of the Institute of Materials Physics and Chemistry in Strasbourg employed a "femtosecond" laser, using ultra-fast bursts of laser light, to alter electron spin and thus speed up retrieval and storage.
"Our method is called the photonics of spin, because it is photons [particles of light] that modify the state of the electrons' magnetisation" on the storage surface, Bigot told AFP.
Data is retrieved with a burst that lasts just a millionth of a billionth of a second, said Bigot.
Femtosecond lasers currently measure around 30 centimetres (12 inches) by 10 centimetres (four inches) which means they are too big for consumer electronics, he cautioned.
Bigot added, though, that their miniaturisation is likely to be achieved over the next decade.
IBM, Hitachi and other corporations are "extremely interested" by the research, Bigot said.