R. V. Mikhaylovskiy (SIMES Seminar)

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

Location
Room 335, McCullough Building

Category(ies)


Note that this seminar will be held at Stanford.

TERAHERTZ SPECTROSCOPY OF ULTRAFAST SPIN DYNAMICS

 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.