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张国平教授学术报告会 - 12月21日
发表时间:2017-12-19 阅读次数:757次

报告时间:1221日,14:00 - 15:30

报告地点:物理楼138

Title:Laser-induced femtosecond demagnetization and all-optical spin switching

 

Abstract 
Since the pioneering experiment by the Beaurepaire and Bigot group in 1996, none had expected then that femtomagnetism has so much impact on the magnetism research today.  Experimentally, they showed that an ultrashort 60-fs laser pulse could reduce the magnetic spin moment of fcc Ni within 1 ps, literally bypassing the phonon bottleneck. Thus, it is very puzzling from the theoretical point of view how the spin moment can drop so quickly. The entire process is nonlinear, nonequilibrium, and ultrafast.  Before one could theoretically understand the entire process, the field took another turn and all-optical spin reversal was discovered, where a single laser pulse can switch spin from up to down and from down to up, without a magnetic field. This represents an important paradigm shift. To this end, the spin switching is found mainly in ferrimagnets.  In October 2017, Bigot's group demonstrated a first spin reversal in a true ferromagnet.  In this talk I will discuss femtomagnetism with emphasis on the latest developments in ultrafast magnetic storage on several hundred nanometer scales and all-optical spin switching devices for wireless communication.
 
 
References
1. E. Beaurepaire, J. -C. Merle, A. Daunois and J.-Y. Bigot, Ultrafast spin dynamics in ferromagnetic nickel, Phys. Rev. Lett. {\bf 76}, 4250 (1996).
2. G. P. Zhang and W. H\"ubner, Laser-induced ultrafast demagnetization in ferromagnetic metals, Phys. Rev. Lett.  {\bf 85}, 3025 (2000).
3.  G. P. Zhang, W. H\"ubner, E.  Beaurepaire and J.-Y. Bigot, {\it Laser-induced ultrafast demagnetization: Femtomagnetism, A new frontier?}  Topics Appl. Phys.  {\bf 83}, 245-289 (2002).
4. G. P. Zhang, W. H\"ubner, Georgios Lefkidis, Yihua Bai, and T. F. George, Paradigm of the time-resolved magneto-optical Kerr effect for femtosecond magnetism, Nature Physics {\bf 5}, 499, (2009).
5. G. P. Zhang, Y. H. Bai and T. F. George, {\it Switching ferromagnetic spins by an ultrafast laser pulse: Emergence of giant optical spin-orbit torque}, EPL {\bf 115}, 57003   (2016).
6.  G. P. Zhang, T. Latta, Z. Babyak, Y. H. Bai, and T.  F. George, {\it All-optical spin switching: A new frontier in femtomagnetism — A short review and a simple theory}, Modern Physics Letters B {\bf 30}, 16300052 (2016).
7. Yuhang Ren, Wei Lai, Zehra Cevher, Yu Gong, and G. P. Zhang, {\it Experimental demonstration of 55-fs spin canting in photoexcited iron nanoarrays},  Appl. Phys. Lett. {\bf 110}, 082404 (2017).
8.  G. P. Zhang, T. Jenkins, M. Bennett and Y. H. Bai, {\it Manifestation of intra-atomic 5d6s-4f exchange coupling in photoexcited gadolinium }, J. Phys.: Condens. Matter {\bf 29}, 495807 (2017).

 

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