Coherent Control of the Route of an Ultrafast Magnetic Phase Transition via Low-Amplitude Spin Precession

Abstract

Time-resolved magneto-optical imaging of laser-excited rare-earth orthoferrite ðSmPrÞFeO 3 demonstrates that a single 60 fs circularly polarized laser pulse is capable of creating a magnetic domain on a picosecond time scale with a magnetization direction determined by the helicity of light. Depending on the light intensity and sample temperature, pulses of the same helicity can create domains with opposite magnetizations. We argue that this phenomenon relies on a twofold effect of light which (i) instantaneously excites coherent low-amplitude spin precession and (ii) triggers a spin reorientation phase transition. The former dynamically breaks the equivalence between two otherwise degenerate states with opposite magnetizations in the high-temperature phase and thus controls the route of the phase transition.

Manipulation of ferromagnets via the spin-selective optical Stark effect

“…Recent experiments on the ferrimagnetic metallic alloy GdFeCo found optical magnetization switching without light polarization in a certain range of light intensities and sample temperatures, casting doubt on the ubiquity of the IFE. 19 Such a behavior was not reported for TbCo films, however. 20 In this paper, we predict huge effective magnetic fields induced by the below-band-gap polarized light through the spin-selective ac (optical) Stark effect, 21 i.e., the shift of electronic energy levels connected through finite optical matrix elements.…”

Irreversible magnetization switching using surface acoustic waves

“…A short perturbation (e.g an optical 15,16 , acoustic 3 , or ultra-fast magnetic 17 or electric 18 field pulse) then modifies the micromagnetic parameters enough to change the effective field seen by the magnetization, and send it precessing. If the precession amplitude is sufficiently large, the magnetization can switch to another potential valley, where it will remain if the perturbation lasts an odd multiple of half the precession period 17 , or if damping eventually prevents M from oscillating between the two minima ("ringing" phenomenon).…”

Terahertz emission spectroscopy of laser-induced spin dynamics inTmFeO3andErFeO3orthoferrites

“…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.…”