Femtosecond laser pulse induced magnetization reversal : Towards thermo-magnetic writing at THz rates (Invited Paper)

概要

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The ultimate speed limit of thermo-magnetic writing is investigated by time-resolved measurements of femtosecond laser pulse induced magnetization reversal in amorphous Gd_<23.1>Fe_<71.9>Co_<5.0>. We prove the resulting reversal dynamics to be governed by the product of two independent processes - the temperature induced changes of the magnetization magnitude times the magnetic field driven reversal of its orientation. Based on this factorization, purely magnetic reversal times are derived from the data. These times show no variation with temperature, but tremendously decrease from several tens of nanoseconds down to only a few picoseconds with increasing excitation density. A minimum reversal time of about 2 ps is found that indicates the possibility of THz thermo-magnetic writing rates. However, the slow cooling of the heated sample limited the maximum achievable writing rates to the GHz range. Only slight improvement of the cooling rates is found when substrates with almost perfect electronic (gold) or phononic (sapphire) heat conductivity are used as heat sinks.
社団法人日本磁気学会の論文
2002-10-01