All‐Optical Helicity‐Dependent Switching in Hybrid Metal–Ferromagnet Thin Films

Abstract

Over the past decades, optical manipulation of magnetization by ultrafast laser pulses has attracted extensive interest. It not only shows intriguing fundamental science arising from the interactions between spins, electrons, phonons and photons, but also manifests the potential to process and store data at a speed that is three orders of magnitude faster than the current technologies. In this paper, we experimentally demonstrate all-optical helicity-dependent switching (AO-HDS) in hybrid metalferromagnet thin films, which consist of Co/Pt multilayers with perpendicular magnetic anisotropy and an Au film capping layer on the top. We have systematically studied the switching behaviors of the hybrid Co/Pt-Au material, with various laser repetition rates, scanning speeds and fluences. In comparison with bare Co/Pt multilayers, the hybrid metal-ferromagnet thin films show pronounced AO-HDS when the number of laser pulses per along the scanning direction gradually increases. In addition, the AO-HDS effect is very robust against laser fluences. We have further proposed a possible mechanism based on numerical simulations of the opto-magnetic coupling model, which indicate that the benefits of the Au layer in the AO-HDS process are twofold: serving as a good heat sink and substantially prolonging the effective magnetic field induced by the inverse Faraday effect. Our findings promise a new material system that exhibits stable AO-HDS phenomena, and hence could transform future magnetic storage devices, especially with the addition of plasmonic nanostructures made of noble metals.

Helicity‐Preserving Metasurfaces for Magneto‐Optical Enhancement in Ferromagnetic [Pt/Co]N Films

“…demonstrated AO‐HDS with unpatterned Au capping layers over Ta 3/Pt 0.7/[Co 0.8/Pt 0.8] 3 /Ta 3 (in nm). [ 54 ] A minimum laser fluence of 3.01 mJ cm −2 was necessary to induce all‐optical switching with 50 nm thick Au layers compared to 0.296 mJ cm −2 in the ferromagnetic films without Au cladding. However, helicity dependence was observed over a wide fluence window spanning ≈10 mJ cm −2 in Au‐capped magnetic layers, while clear helicity‐dependent switching was not seen in bare films.…”

Ultrafast optical manipulation of magnetic order in ferromagnetic materials

“…Figure c, d , and e are reproduced with permission from ref. [ 116 ], Copyright (2020) WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim. Figure f is reproduced with permission from ref.…”

“…The result shows that the switching requires a minimal 0.15 ps duration of IFE field with an extreme value of around 20 T. Similar results were also found in FePt [ 112 , 115 ]. Recently, we found that the generated effective magnetic field can be prolonged in Co/Pt-Au heterostructures [ 116 , 117 ]. Based on the classic Lenz’s law, the decrease of the IFE-induced magnetic field wakes a loop current in the Au top-cladding layer.…”

“…Only 4 pulse pairs could completely switch a Pt/Co/Pt stack using the dual-pulse approach [ 106 ]. Taking advantage of laser-induced contributions, such as harnessing spin-polarized hot electrons [ 107 , 108 ] and enhancing opto-magnetic effect [ 116 ], could help us to further push AO-HDS of ferromagnetic materials. On the other hand, the cumulative AOS may benefit the design of neuromorphic architectures [ 128 , 129 ].…”

Organic magnetoelectric and optomagnetic couplings: perspectives for organic spin optoelectronics

“…Owing to the development of electronic devices toward miniaturization and high integration, optomagnetic and magnetoelectric materials are of growing interest in the fields of sensors and memory, where they allow control of the magnetization (or polarization) by an external field [1][2][3][4][5][6][7][8] . The charge, orbit, spin, and phonon are strongly coupled, endowing ferromagnetic materials with rich coupling properties, such as magnetoelectric coupling and optomagnetic coupling [9][10][11][12] .…”