Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
Department Seminar
Host: A. Paarmann

Monday, May 15, 2017, 11:00 am
All are invited to meet around 10:40 am for a chat with coffee & cookies.
Willstätter House, Faradayweg 10
Prof. Dr. Andrei Kirilyuk
Atomic Nanostructures group, Spectroscopy of Solids and Interfaces, Institute of Molecules and Materials, Radboud University, Nijmegen
All-optical magnetization switching: mechanisms and time scales
While the basic possibilities for direct laser manipulation of magnetization have been indicated a long time ago, only recently it became possible to apply such control in magnetically ordered materials. The first breakthrough was a direct demonstration of all- optical magnetic recording by single fs pulses in ferrimagnetic GdFeCo alloys [1]. In spite of the fact that the switching was reproducible and robust, the exact process and mechanism of it remained elusive for a long time. After extensive research, single-pulse switching of the magnetization in ferrimagnetic alloys and multilayers was identified as a combination of ultrafast laser-induced demagnetization with the angular-momentum conservation in the exchanged-coupled sublattices of a ferrimagnet, on a sub-picosecond time scale [2].
Intriguingly, recently it has been demonstrated that several of ferromagnetic multilayers can be switched by circularly polarized light [3]. In this case, the observation indicate a rather different mechanism than that of the ferrimagnetic samples. Indications of accumulated multi-pulse effect seem to be in agreement with the earlier simulations based on the inverse Faraday effect [4], that also show the importance of increased pulse width.
Moreover, we have recently discovered the possibility of ultrafast photo-magnetic recording in transparent dielectrics [5] based on a charge-transfer modification of magnetocrystalline anisotropy, a direct non-thermal process. Changing the polarization of the laser pulse we deterministically steer the magnetization in the garnet, writing magnetic domains at will. This mechanism allows ever fastest write-read magnetic recording event (<20 ps) accompanied by unprecedentedly low heat load.
[1] C.D. Stanciu et al., Phys. Rev. Lett. 99, 047601 (2007)..
[2] A. Kirilyuk, A.V. Kimel, and Th. Rasing, Rep. Prog. Phys. 76 , 026501 (2013). [3] C.-H. Lambert et al, Science 345, 1337 (2014).
[4] K. Vahaplar et al, Phys. Rev. Lett. 103, 117201 (2009).
[5] A. Stupakiewicz et al., Nature 542, 71 (2017)..