Fyzikální ústav Akademie věd ČR

Seminář Úterý, 04.03.2014 15:00

Přednášející: Karel Carva (Oddělení teoretické fyziky, katedry fyziky kondenzovaných látek, MFF UK)
Místo: Na Slovance, přednáškový sál v přízemí
Jazyk: anglicky
Pořadatelé: Oddělení teorie kondenzovaných látek

Abstract: In recent years it has been demonstrated that magnetization can be changed without applying an external magnetic field in extremely short timescales of the order of hundreds of femtoseconds [1]. We have studied the effect by means of ab initio calculations for three ferromagnetic metals Fe, Co and Ni [2] considering the Elliott-Yafet electron-phonon spin-flip (SF) scattering [3] which has been suggested to be the dominant microscopic mechanism. We also show that the density of states and the energy-dependence of the SF probability have to be included accurately in calculations. Recently 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 standard explanations used for demagnetization. We calculate intraatomic exchange between Gd 4f and 5d orbitals 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 [4].

[1] E. Beaurepaire, J.-C. Merle, A. Daunois J.-Y. Bigot, Phys. Rev. Lett. 76, 4250 (1996).
[2] K. Carva, M. Battiatio, D. Legut, P.M. Oppeneer, Phys. Rev. B 87, 184425 (2013).
[3] K. Carva, M. Battiato, P. M. Oppeneer, Phys. Rev. Lett., 107, 207201 (2011).
[4] S. Wienholdt, D. Hinzke, K. Carva and others, Phys. Rev. B 88, 020406(R) (2013).