Theoretical seminar | 16 February 2022

Terahertz (THz) electro-magnetic radiation has a direct access to electron spins in solids. As the meV photon energy at THz frequencies matches the energy scale of the magnetic exchange and spin-orbit interactions, the terahertz waves can probe and control ultrafast magnetization dynamics. Yet, until recently potential of THz radiation has not been utilized in the field of magnetism.
In my talk I will explain how THz emission spectroscopy can be applied as an ultrafast magnetometer allowing to trace picosecond spin dynamics and a femtosecond amperemeter for spin-polarized currents. These developments allowed us to discover light-induced modification of the exchange interaction in a broad class of antiferromagnetic oxides [1] and generation of spin-polarized photo-currents at interfaces of metallic magnetic heterostructures [2].
In the second part of my talk I will discuss the potential of intense THz-radiation to control spins in magnetic materials. An efficient mechanism for such a control based on interplay between rare-earth orbitals and transition metal spins in antiferromagnetic insulators will be suggested [3]. Particularly, by resonant pumping low-energy rare-earth orbitals one can manipulate magnetic anisotropy, which in turn can efficiently drive spin motion in nonlinear regime [4]. The strength of the THz-driven anisotropy torque can exceed the Zeeman torque exerted by the magnetic field by at least one order of magnitude. By further increasing the anisotropy torque with the help of plasmonic THz antennas, in our latest measurements we indicate that the THz-driven magnetization switching can be indeed achieved in the experiment. In this way the magnetic recording at THz clock rates is made feasible.

Main paper/arXiv, related to the seminar, and other references

1. S. Schlauderer, C. Lange, S. Baierl, T. Ebnet, C. P. Schmid, D. C. Valovcin, A. K. Zvezdin, A. V. Kimel, R. V. Mikhaylovskiy* and R. Huber. “Temporal and spectral fingerprints of ultrafast all-coherent spin switching”. Nature 569, 383 (2019).
2. S. Baierl, M. Hohenleutner, T. Kampfrath, A. K. Zvezdin, A. V. Kimel, R. Huber, and R. V. Mikhaylovskiy. “Nonlinear spin control by terahertz driven anisotropy fields”. Nature Photonics 10, 715 (2016).
3. T. J. Huisman, R. V. Mikhaylovskiy, J. D. Costa, F. Freimuth, E. Paz, J. Ventura, P. P. Freitas, S. Blügel, Y. Mokrousov, Th. Rasing and A. V. Kimel. “Femtosecond control of electric currents in metallic ferromagnetic heterostructures”. Nature Nanotechnology 11, 455 (2016).
4. R. R. Subkhangulov, R. V. Mikhaylovskiy, A. K. Zvezdin, V. V. Kruglyak, Th. Rasing and A. V. Kimel. Terahertz modulation of the Faraday rotation by laser pulses via the optical Kerr effect. Nature Photonics 10, 111 (2016)
5. R. V. Mikhaylovskiy, E. Hendry, A. Secchi, J. H. Mentink, M. Eckstein, A. Wu, R. V. Pisarev, V. V. Kruglyak, M. I. Katsnelson, Th. Rasing and A. V. Kimel. “Ultrafast optical modification of exchange interactions in iron oxides”. Nature Communications 6, 8190 (2015)