All-optical magnetization reversal by circularly polarized laser pulses: Experiment and multiscale modeling

Abstract

We present results of detailed experimental and theoretical studies of all-optical magnetization reversal by single circularly-polarized laser pulses in ferrimagnetic rare earth-transition metal (RE-TM) alloys Gd x Fe 90−x Co 10 (20% < x < 28%). Using single-shot time-resolved magneto-optical microscopy and multiscale simulations, we identified and described the unconventional path followed by the magnetization during the reversal process. This reversal does not involve precessional motion of magnetization but is governed by the longitudinal relaxation and thus has a linear character. We demonstrate that this all-optically driven linear reversal can be modeled as a result of a two-fold impact of the laser pulse on the medium. First, due to absorption of the light and ultrafast laser-induced heating, the medium is brought to a highly nonequilibrium state. Simultaneously, due to the ultrafast inverse Faraday effect the circularly polarized laser pulse acts as an effective magnetic field of the amplitude up to ∼20 T. We show that the polarization-dependent reversal triggered by the circularly polarized light is feasible only in a narrow range (below 10%) of laser fluences. The duration of the laser pulse required for the reversal can be varied from ∼40 fs up to at least ∼1700 fs. We also investigate experimentally the role of the ferrimagnetic properties of GdFeCo in the all-optical reversal. In particular, the optimal conditions for the all-optical reversal are achieved just below the ferrimagnetic compensation temperature, where the magnetic information can be all-optically written by a laser pulse of minimal fluence and read out within just 30 ps. We argue that this is the fastest write-read event demonstrated for magnetic recording so far.

Efficiency of ultrafast laser-induced demagnetization in GdxFe100−x−yCoMedapalli1, Razdolski2, Savoini3 et al. 2012Phys. Rev. BSelf Cite333265View full textAdd to dashboardCite

“…A comparison of the degree of demagnetization in Gd 18 FeCo and Gd 30 FeCo with that of Gd 24 FeCo shows that the more effective demagnetization takes place when the magnetizations of the individual atomic sublattices (Fe and Gd) are approximately equal. Finally, we would like to note that since achieving the conditions for 100% demagnetization is of crucial importance for the realization of all-optical switching via a strongly nonequilibrium state, 16,17,20 our results clearly show that the all-optical switching is most easily observed in ferrimagnets with a magnetic compensation point. All-optical switching requires less laser pulse fluence when the sample is below the compensation temperature.…”

“…15 It is also obvious that, in order to reach an efficient optical control of magnetism in a medium, one should achieve proper conditions for a complete demagnetization or, better, magnetization reversal. [16][17][18][19][20] Indeed, it was demonstrated recently that if a rare earth (RE)-transition metal (TM) ferrimagnet, having antiferromagnetically coupled nonequivalent RE and TM magnetic sublattices, is brought into a transient state with no net magnetization on a subpicosecond time scale, the subsequent relaxation from this state leads to a deterministic reversal of the initial net magnetization of the medium 17 if the absorbed energy is great enough. 21 These and earlier results of all-optical magnetization reversal in Gd x Fe 100−x−y Co y alloys 18,19 logically lead to the question why these RE-TM alloys show such interesting and useful properties.…”

“…Several parameters of the switching process appear to depend on Gd concentration, which is not well understood so far. 20 Therefore, understanding how the ultrafast demagnetization of RE-TM alloys depends on Gd concentration, temperature of the sample, and pump fluence is an important and timely issue.…”

Manipulation of ferromagnets via the spin-selective optical Stark effect

“…8,11,12 Several theoretical mechanisms have been proposed, such as the optical Barnett effect or the inverse Einstein-de Haas effect, 13 light-induced circular currents in the collisionless limit, 14,15 the impulsive stimulated Ramanlike process, 8 and photonic angular momentum transfer via deflection of the scattered photons. 16 A dissipative IFE under THz irradiation has been computed for dirty metals with extrinsic spin-orbit interaction.…”

Ab InitioTheory of Coherent Laser-Induced Magnetization in Metals

“…Notably, for nonmagnetic metals the largest induced magnetizations are obtained for materials with large SOC, like Au and Pt. In previous work the IFE has not been treated as an induced magnetization, but as an effective optomagnetic field B opt [1,5,20]. In this way the influence of the IFE on a magnetic material has been described as an effective Zeeman field B opt · M i acting on the atomic spin moment M i with unchanged length [17,20].…”