R. V. Mikhaylovskiy (SIMES Seminar)

Date(s) - Oct 31 2014
11:00 AM - 12:00 PM

Room 335, McCullough Building


Note that this seminar will be held at Stanford.


 R. V. Mikhaylovskiy

Radboud University Nijmegen, the Netherlands

Terahertz emission spectroscopy represents a unique tool that provides novel information about ultrafast spin dynamics not accessible by any other methods.In such experiments one detects electro-magnetic radiation at THz frequencies emitted from a sample that is excited by ultrafast optical laser pulses.The exceptional efficiency of THz emission spectroscopy is evidenced by the first ever demonstrations of femtosecond laser excitation of high-frequency quasi-antiferromagnetic spin-wave modes in a broad class of iron oxides including hematite and rare-earth dynamics in the orthoferrites.

I will demonstrate both experimentally and theoretically that the ratio between the antisymmetric and symmetric exchange components can be manipulated via ultrafast, sub-picosecond laser excitation of iron oxides. The resulting coherent spin oscillations lead to THz emission and from its strength we estimate that a sub-picosecond laser pulse with a moderate fluence of ~ 1 mJ/cm2 acts as a pulsed magnetic field of 0.01 Tesla that corresponds to the change of the exchange energy of over 10 nJ.

Finally, I will discuss the role of the rare-earth ions in opto-magnetic effects. In this case the femtosecond dynamics of the magnetic moments is studied in resonantly pumped Dy3+ ions in antiferromagnetic DyFeO3. Due to the d−f exchange coupling between the spins of Fe3+ and Dy3+ the laser-induced magnetization of Dy3+ can impulsively excite Fe3+ spin waves. Furthermore, by varying the polarization of the optical pump we achieved the selective excitation of electric dipole and magnetic dipole components of the crystal field resonances of Er3+ ions in the ErFeO3 antiferromagnet.