Laser-induced ultrafast spin dynamics in ErFeO3

Abstract

Using 100-fs optical laser pulses, we have been able to excite and probe spin dynamics in the rare-earth orthoferrite ErFeO 3 . The investigation was performed in a broad temperature range with the focus on the vicinities of the compensation point T comp ≈ 47 K and the spin reorientation transition region in the interval 86 K T 99 K. Spin precession excited by the laser pulse was present in a large part of the investigated temperature range, but was especially strong near the spin reorientation region. In this region the laser pulse also caused an ultrafast spin reorientation. By changing the laser pulse fluence, we could vary both the reorientation amplitude and the reorientation speed. We show that the laser-induced spin dynamics in ErFeO 3 is caused in part by heating and in part by the inverse Faraday effect. Comparing to the results of similar experiments in other rare-earth orthoferrites, we found the speed of the laser-induced spin reorientation to be significantly lower. We attribute this finding to the weaker electron-phonon coupling of the Er 3+ 4f electrons with the lattice.

Terahertz emission spectroscopy of laser-induced spin dynamics inTmFeO3andErFeO3orthoferrites

“…Following excitation by femtosecond optical pulses with a peak fluence of ∼10 mJ/cm 2 and focused to spot of ß1 mm radius, TmFeO 3 and ErFeO 3 demonstrate ultrafast spin-reorientation dynamics, which we resolve by monitoring THz emission signals. We show that the THz emission spectroscopy serves as an alternative and complementary tool with respect to the more conventional all-optical pump-probe spectroscopy applied to study these materials previously [10][11][12]. Moreover, the power of this technique is evidenced here by the observation of an as yet unobserved optical excitation of dipole active modes in the vicinity of the spin-reorientation phase transition.…”

“…The spectral component at 0.1 THz, which we assign to the quasi-ferromagnetic mode of the iron sublattices, is excited in the relatively narrow temperature interval between 50 and 70 K. It is natural to assume that this mode is excited just below the spin-reorientation temperature range, as was observed in optical experiments [10][11][12]. The shift of ß20 K from the spin-reorientation region (80-90 K) is due to the steady-state temperature buildup via cumulative laser heating.…”

“…Conversely, laser-induced spin dynamics in magnetic materials is also accompanied by emission of the THz radiation [29][30][31][32][33][34][35][36]. Here we show that THz emission spectroscopy provides novel information about ultrafast laser-induced spin dynamics in TmFeO 3 and ErFeO 3 orthoferrites which is not accessible by more common all-optical methods [10][11][12]. The power of the method is evidenced by the fact that, in addition to the expected quasi-ferromagnetic and quasi-antiferromagnetic modes of the iron sublattices, the THz emission spectroscopy enables detection of an optically excited resonance at an unexpected frequency of ß0.3-0.35 THz.…”

“…In these experiments, a femtosecond laser pump pulse excites the magnetic medium, while another laser pulse, delayed with respect to the pump, probes the photo-induced magnetic changes via the magneto-optical Faraday and/or Cotton-Mouton effects. Examples of successful studies of these types are the ultrafast light-induced spin reorientation in antiferromagnets [10][11][12][13], ultrafast inverse Faraday effect [14][15][16], and inertia-driven switching [17]. However, a substantial limitation of these techniques lies in the fact that visible light cannot interact with spins directly, enabling access only to those spin resonances that efficiently couple to the orbital degree of freedom via the spin-orbit interaction.…”

Dynamics of laser-induced spin reorientation in Co/SmFeO3heterostructure

“…The few studies done show a maximum 20 • reorientation. 35,[43][44][45] It seems that ultrafast laser heating is not equivalent to slow heating. Such an effect has been reported in another system has well, 46 where it was suggested that the laser pulse brings the system into a metastable state not accessible otherwise.…”