Opportunities in High-Frequency and Ultrafast Dynamics of Magnets, Semiconductors and Beyond

Guo-ping Zhang

Department of Physics, Indiana State University, Terre Haute, IN 47809

High-frequency and ultrafast dynamics is an emerging field.  It presents tremendous new challenges and new opportunities. Its potential impact is huge.  High-frequency detectors are just one example. The fast dynamics has also been observed in superconductors, semiconductors, chemical reactions, photosynthesis and many others. In this talk, I will discuss the latest breakthrough in THZ spin dynamics in  magnets. The conventional demagnetization process (spin precession, magnetic domain motion and rotation) is mainly governed by spin-lattice, magnetic dipole and Zeeman, and spin-spin interactions. It occurs on a time scale of nanoseconds.  Technologically, it is always advantageous to have much faster magnetization changes in order to improve the data processing speed. Unfortunately, the present speed of magnetic devices is already up to the limit of the conventional mechanism with little room left.  Fortunately and unprecedentedly, recent experimental investigations have demonstrated a much faster magnetization dynamics which occurs on a femtosecond time scale. This would present a new opportunity for magnetism: Femto/Tera-magnetism. Finally, if time permits, I will present some results in THZ dynamics in semiconductors and, in particular, in C60.

References:

(1) Laser-induced Ultrafast Demagnetization: Femtomagnetism, A New Frontier?  \\ G. P. Zhang, W. H\"ubner, E.  Beaurepaire and J.-Y. Bigot, Spin Dynamics in Confined Magnetic Structures {\bf 83}, 245-289 (2001), edited by K. Ounadjela, B. Hillebrands.

(2) Laser-induced ultrafast demagnetization in ferromagnetic metals, G. P. Zhang and W. H\"ubner, Phys. Rev. Lett. {\bf 85}, 3025 (2000).

(3)  Laser-control of ferro- and antiferromagnetism\\ M. Trzeciecki, O. Ney, G. P. Zhang and W. H\"ubner, Advances in
Solid State Physics {\bf 41}, 547-555 (2001).

(4) Ultrafast spin dynamics in ferromagnetic Nickel\\ W. H\"ubner and G. P. Zhang, \PRB {\bf 58}, R5920 (1998).

(5) Femtosecond electron and spin dynamics probed by nonlinear optics\\ G. P. Zhang and W. H\"ubner, Appl. Phys. B -Lasers and Optics {\bf 68}, 495 (1999).

(6) Femtosecond spin dynamics in the time domain\\ G. P. Zhang and W. H\"ubner, J. Appl. Phys. {\bf 85}, 5657 (1999).

(7) Femtosecond spin dynamics probed by linear and nonlinear magneto-optics\\ W. H\"ubner and G. P. Zhang, J. of Magn. Magn. Mater. {\bf 189}, 101 (1998).

(8) Towards higher-temperature superconductivy in ${\rm C_{60}}$\\ G. P. Zhang, X. Sun and T. F. George, {\it Modern Topics in Chemical Physics}, edited by T. F. George, X. Sun and G. P. Zhang, {\it Research Signpost} (2002).

(9) Origin of giant optical nonlinearity in Charge-transfer Mott insulators: A new paradigm for nonlinear optics\\ G. P. Zhang, Phys. Rev. Lett.  {\bf 86}, 2086-2089 (2001).