Simultaneous measurements of terahertz emission and magneto-optical Kerr effect for resolving ultrafast laser-induced demagnetization dynamics

Abstract

Simultaneous detection of terahertz (THz) emission and transient magneto-optical response is employed to study ultrafast laser-induced magnetization dynamics in three different types of amorphous metallic alloys: Co, GdFeCo, and NdFeCo. A satisfactory agreement between the dynamics revealed with the help of these two techniques is obtained for Co and GdFeCo. For NdFeCo the THz emission indicates faster dynamics than the magneto-optical response. This observation indicates that in addition to spin dynamics of Fe, ultrafast laser excitation of NdFeCo triggers faster magnetization dynamics of Nd originating from its orbital momentum.

THz emission from Co/Pt bilayers with varied roughness, crystal structure, and interface intermixing

“…Together with an intense search for the mechanisms of the ultrafast demagnetization, these first experiments also launched debates about the role of artifacts in ultrafast time-resolved measurements and the validity of the conclusions of these initial experiments [5][6]. These discussions motivated the development of new probes for ultrafast magnetization dynamics and resulted, in particular, in an elegant proposal to employ THz time-domain emission spectroscopy, which relies on the fact that any magnetic dipole change must be accompanied by an emission of electromagnetic radiation [7][8][9]. However, the application of THz time-domain emission spectroscopy for the study of ultrafast magnetization dynamics in magnetic multilayers led to rather unexpected results -the THz electric field emitted as the result of the laser induced demagnetization of Fe/Au and Fe/Ru bilayers was stronger than the THz electric field emitted as the result of the demagnetization of a single Fe-film [10].…”

Charge pumping driven by the laser-induced dynamics of the exchange splitting

“…In a previous work we studied in these two systems already the spin-orbit torques (SOTs), which also require SOI and inversion asymmetry and are therefore loosely related to the effect of interest here. Laser-induced electric currents have been studied experimentally in Co/Pt already [16], while such experiments have not yet been performed in Mn/W(001). However, monolayers of Mn on W(001) have already been prepared experimentally and their magnetic structure has been determined from spin-polarized scanning tunneling microscopy [33].…”

“…(3) contains only this current and misses several contributions that we discussed in the Introduction, namely the current from the conversion of the superdiffusive spin current into an interfacial charge current by the inverse spin Hall effect and the current from the inverse spin-orbit torque and the tilting magnetization due to the inverse Faraday effect. The theoretical modeling of these two currents has been described already elsewhere [3,16].…”

“…By optimizing the composition and layer thicknesses of the magnetic heterostructures one can even achieve THz radiation that is sufficiently strong to make photocurrents in magnetic heterostructures attractive for application in table-top ultrabroadband THz emitters [3]. Additionally, the photocurrents might provide a new and complementary tool to investigate magnetization dynamics at subpicosecond time scales, where other magnetooptical probing techniques face difficulties [14][15][16].…”

Selective Excitation of Terahertz Magnetic and Electric Dipoles in Er3+ Ions by Femtosecond Laser Pulses in ErFeO3Mikhaylovskiy1, Huisman2, Pisarev3 et al. 2017Phys. Rev. Lett.Self Cite370260View full textAdd to dashboardCite

“…The polarizations of the observed components allow us to assign them to the modes of different symmetry in accordance with Table I. The transitions within the doublets have frequencies below the cutoff frequency of our THz spectrometer (∼100 GHz) [30] and are not resolved here.…”