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Laser-Rewriteable Ferromagnetism at Thin Film Surfaces

Ehrler, J.; He, M.; Shugaev, M. V.; Polushkin, N. I.; Wintz, S.; Liersch, V.; Cornelius, S.; Hübner, R.; Potzger, K.; Lindner, J.; Fassbender, J.; Ünal, A. A.; Valencia, S.; Kronast, F.; Zhigilei, L. V.; Bali, R.


Manipulation of magnetism using laser light is considered a key to the advancement of data storage technologies. Until now, most approaches seek to optically switch the direction of magnetization rather than to reversibly manipulate the ferromagnetism itself. Here we use ~100 fs laser pulses to reversibly switch ferromagnetic ordering on and off by exploiting a chemical order-disorder phase transition in Fe60Al40, from the B2 to the A2 structure and vice versa. A single laser pulse above a threshold fluence causes non-ferromagnetic B2 Fe60Al40 to disorder and form the ferromagnetic A2 structure. Subsequent pulsing below the threshold reverses the surface to B2 Fe60Al40, erasing the laser induced ferromagnetism. Simulations reveal that the order-disorder transition is regulated by the extent of surface supercooling; above threshold the film melts-through and the consequent stability of the supercooled liquid phase suppresses vacancy diffusion, freezing the material into the disordered state. Pulsing below threshold forms a limited supercooled surface phase that solidifies at sufficiently high temperatures, enabling diffusion assisted reordering. This demonstrates that ultrafast lasers can achieve subtle atomic rearrangements in bimetallic alloys in a reversible and non-volatile fashion.

Keywords: magneto-optical devices; data storage; phase transitions; fs laser modifications; supercooling; order-disorder

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