Speaker
Dr
Karel Carva
(Department of Condensed Matter Physics, Charles University)
Description
Since the first demonstration of femtosecond laser-induced demagnetization in
1996 [1], optical manipulation of magnetization has developed into a vibrant
area of research that has explosively grown over the last decade. The most
interesting one of discoveries is the demonstration of all-optical magnetization
reversal and opto-magnetic recording with femtosecond laser pulses. All-optical
magnetization switching (AOS) is emerging as a novel magnetic recording
technology, its potential has been fully recognized by the magnetic recording
industry, which enlisted AOS process on its roadmap towards ultra-high
magnetic recording densities beyond 1 Tb/in^{2}.
One of the critical problems in this field is related to the character of the
transiently demagnetized state. Recently an insight into this problem has been
provided by novel optical methods based on high harmonics generation [2].
Measurements of time-, energy-, and angle-resolved T-MOKE magnetic
asymmetry spectra at M-edges have been compared to ab initio predictions for
different deviations from the magnetic ground state, which allows us to draw
conclusions about the importance of transversal magnetic excitations in the
ultrafast laser-induced demagnetization [3].
An interesting magnetization dynamics has been observed in systems with 2
ferrimagnetically ordered sublattices: a complete reversal of magnetization in
GdFeCo alloy. Most magnetic momentum in the system originates from Gd 4f
states deep below the Fermi level, which prevents direct access to it by the laser.
We calculate intraatomic exchange between Gd 4f and 5d orbitals [4] to allow
mapping the problem to an effective orbital-resolved Heisenberg Hamiltonian. A
subsequent simulation based on the LLG equation has reproduced the switching
behavior and shown that the exchange coupling is sufficient to revert the large
moment of Gd 4f shell on a ps time scale [5].
[1] E. Beaurepaire, J.-C. Merle, A. Daunois J.-Y. Bigot, Phys. Rev. Lett. 76, 4250 (1996).
[2] Fan, T., et al., Proceedings of the National Academy of Sciences 112, pp. 14206–14211 (2015)
[3] E. Turgut et al., Phys. Rev. B 94, 220408(R) (2016).
[4] B. Frietsch et al., Nat. Commun. 6, 8262 (2015).
[5] S. Wienholdt, D. Hinzke, K. Carva and others, Phys. Rev. B 88, 020406(R) (2013).
Primary authors
Dr
Dominik Legut
(IT4I)
Dr
Karel Carva
(Department of Condensed Matter Physics, Charles University)
Prof.
Peter Oppeneer
(Department of Physics and Astronomy, Uppsala University)
