All-optical switching of magnetic storage media has been widely believed to be impossible due to the insufficient angular momentum of photons. Now, researchers at Nijmegen University (Nijmegen, Netherlands) have demonstrated that magnetization can indeed be reversed experimentally by light at ultrafast speeds. The scientists used a single 40 fs circularly polarized laser pulse to permanently reverse magnetization in the ferromagnetic alloy gadolinium iron cobalt (Gd22Fe74.6Co3.4), a material useful for data storage.
This optically induced ultrafast magnetization reversal is the combined result of femtosecond-laser heating of the magnetic system to just below the Curie point of 500 K for GdFeCo, and the circularly polarized 800 nm laser light simultaneously acting as a magnetic field. The Ti:sapphire laser beam is scanned across the sample while the left- and right-circular polarization of the beam is simultaneously modulated. The final state of the magnetization is stable and can be unambiguously determined by the helicity of the laser pulse. The group estimates that the technique enables subpicosecond switching speeds, a result that could improve storage capability in devices such as hard-disk drives, magneto-resistive random access memory, and magneto-optical disks. Contact Claudiu Stanciu at [email protected].