Ultrafast nonthermal photo-magnetic recording in transparent medium

Finding a conceptually new way to control the magnetic state of media with the lowest possible production of heat and simultaneously at the fastest possible speeds is a new challenge in fundamental magnetism1–5. Recent results demonstrate that exclusively in metals it is possible to switch the magnetization between two stable states, and thus to record magnetic bits, by femtosecond circularly polarized laser pulses6–8. However, the switching mechanisms in these materials are directly related to laser-induced heating close to the Curie temperature9–12. While several possibilities for nonthermal all-optical switching in magnetic dielectrics have been discussed13,14, no recording was demonstrated. Here we report about ultrafast all-optical photo-magnetic recording in dielectrics. In ferrimagnetic Co-substituted garnet film, a single linearly polarized femtosecond laser pulse resonantly pumps specific d–d transitions in the Co-ions, breaking the degeneracy between metastable magnetic states. By changing the polarization of the laser pulse, we deterministically steer the net magnetization in the garnet, thus writing ”0” and “1” magnetic bits at will. This mechanism outperforms existing alternatives allowing the fastest write-read magnetic recording event (< 20 ps) accompanied by unprecedentedly low heat load (< 6 J cm(-3)).