All-optical magnetization reversal with femtosecond laser pulses facilitates the fastest and least dissipative magnetic recording, but writing magnetic bits with spatial resolution better than the wavelength of light has so far been seen as a major challenge. Here, we demonstrate that a single femtosecond laser pulse of wavelength 800 nm can be used to toggle the magnetization exclusively within one of two 10-nm thick magnetic nanolayers, separated by just 80 nm, without affecting the other one. The choice of the addressed layer is enabled by the excitation of a plasmon-polariton at a targeted interface of the nanostructure, and realized merely by rotating the polarization-axis of the linearly-polarized ultrashort optical pulse by 90°. Our results unveil a robust tool that can be deployed to reliably switch magnetization in targeted nanolayers of heterostructures, and paves the way to increasing the storage density of opto-magnetic recording by a factor of at least 2. The density of magnetic storage media is limited by the superparamagnetic limit when scaling down magnetic bits. Here, the authors open the way for stacked magnetic storage by using all-optical switching and addressing different magnetic layers by polarization-dependent excitation of plasmon-polaritons.

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Plasmonic layer-selective all-optical switching of magnetization with nanometer resolution

The multifold enhancement of the Faraday effect induced by magnetic dipole and Voigt effect amplification due to electric dipole Mie resonances of the magnetophotonic metasurface is demonstrated. The values of the magneto-optical responses up to 0.8° and 0.5% are experimentally observed for the metasurface with an ultrathin ferromagnetic layer. The results can be used for the development of novel active magnetophotonic metadevices.

Enhanced magneto-optical effects in hybrid Ni-Si metasurfaces

We analytically and numerically investigate magneto-plasmons in metal films surrounded by a ferromagnetic dielectric. In such waveguide using a metal film with a thickness exceeding the Skin depth, an external magnetic field in the transverse direction can induce a significant spatial asymmetry of mode distribution. Superposition of the odd and the even asymmetric modes over a distance leads to a concentration of the energy on one interface which is switched to the other interface by the magnetic field reversal. The requested magnitude of magnetization is exponentially reduced with the increase of the metal film thickness. Based on this phenomenon, we propose a waveguide-integrated magnetically controlled switchable plasmonic routers with 99-%-high contrast within the optical bandwidth of tens of THz. This configuration can also operate as a magneto-plasmonic modulator.

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Switchable plasmonic routers controlled by external magnetic fields by using magneto-plasmonic waveguides.

In this Rapid Communication, we study the generation of quasistatic magnetic fields by the plasmon-induced inverse Faraday effect and present analytical and numerical results for the computation of the induced magnetic field distributions in magnetoplasmonic waveguides. We show that the magnetization of a magnetic area can be reversed within sub-picosecond time in nanoconfined magnetoplasmonic waveguides by surface plasmon polaritions (SPP) and the magnetization can be switched back by a SPP propagating into the opposite direction. In addition, we study a magneto-optical dielectric cavity side coupled to a metal-insulator-metal (MIM) waveguide and show that magnetization switching can be implemented in this structure by SPPs generated by two-frequency pulses as well as by counterpropagating SPPs. These phenomena could open up a new energy-efficient ultrafast method for nanoconfined all-optical magnetization switching.

All-optical magnetization switching by counterpropagataion or two-frequency pulses using the plasmon-induced inverse Faraday effect in magnetoplasmonic structures

Spectroscopic ellipsometry is a prominent method for finding both the thickness and permittivity of unknown thin material films due to its sensitivity, flexibility, and self-referencing nature. For non-absorbing films, the thickness and permittivity can be readily retrieved due to an excess of data content, which produces a clearly defined best-fit for a series of test material parameters. However, in materials with absorption throughout the spectrum, there is often insufficient data content to uniquely characterize both film thickness and permittivity for the thin film material. This leads to a flat fit optimization curve that can produce apparently good fit results from a wide range of material parameters. To overcome this data content shortage, additional techniques are necessary to either increase the measured data content or reduce the unknown parameters and establish the unique material properties for the film. Here, we explore the use of spectroscopic ellipsometry combined with transmission intensity data and discuss the pitfalls of fitting such thin absorbing films. Specifically, we examine the case of titanium nitride, a rising refractory alternative plasmonic material and demonstrate that without proper ellipsometry fitting procedures, retrieved permittivity values can vary by a factor of three or more.

Reliable modeling of ultrathin alternative plasmonic materials using spectroscopic ellipsometry [Invited]

The demand for faster magnetization switching speeds and lower energy consumption has driven the field of spintronics in recent years. The magnetic tunnel junction is the most developed spintronic memory device in which the magnetization of the storage layer is switched by spin-transfer-torque or spin-orbit torque interactions. Whereas these novel spin-torque interactions exemplify the potential of electron-spin-based devices and memory, the switching speed is limited to the ns regime by the precessional motion of the magnetization. All-optical magnetization switching, based on the inverse Faraday effect, has been shown to be an attractive method for achieving magnetization switching at ps speeds. Successful magnetization reversal in thin films has been demonstrated by using circularly polarized light. However, a method for all-optical switching of on-chip nanomagnets in high density memory modules has not been described. In this work we propose to use plasmonics, with CMOS compatible plasmonic materials, to achieve on-chip magnetization reversal in nanomagnets. Plasmonics allows light to be confined in dimensions much smaller than the diffraction limit of light. This in turn, yields higher localized electromagnetic field intensities. In this work, through simulations, we show that using localized surface plasmon resonances, it is possible to couple light to nanomagnets and achieve significantly higher opto-magnetic field values in comparison to free space light excitation.

Surface-plasmon Opto-magnetic Field Enhancement for All-optical Magnetization Switching

We have proposed the use of surface plasmon resonances at the interface of hybrid magneto-photonic heterostructures [Opt. Mat. Express, 7, 4316 (2017)] for all-optical control of the macroscopic spin orientation in nanostructures in fs time scales. This requires strong spin-photon coupling for the resonant enhancement of opto-magnetic fields, generated through the inverse Faraday effect, in magnetic nanostructures with perpendicular anisotropy. Here we report on the development of nm thick interlayers to control the growth orientation of hcp-Co alloys grown on refractory plasmonic materials to align the magnetic axis out-of-plane, thereby meeting key requirements for the realization of ultrafast magneto-photonic devices.

Hybrid magneto photonic material structure for plasmon assisted magnetic switching

Temperature-dependent magnetic transitions in CoCrPt-Ru-CoCrPt synthetic ferrimagnets

We have proposed the use of surface plasmon resonances at the interface of hybrid magneto-photonic heterostructures [Opt Mat Exp, 7, 4316 (2017)] for all-optical control of the macroscopic spin orientation in nanostructures in fs time scales This requires strong spin-photon coupling for the resonant enhancement of opto-magnetic fields, generated through the inverse Faraday effect, in magnetic nanostructures with perpendicular anisotropy Here we report on the development of nm thick interlayers to control the growth orientation of hcp-Co alloys grown on refractory plasmonic materials to align the magnetic axis out-of-plane, thereby meeting key requirements for the realization of ultrafast magneto-photonic devices

Hybrid Magneto Photonic Material Structure for Plasmon Assisted Magnetic Switching

We study, computationally, titanium nitride plasmonic resonators coupled to nanomagnets for magnetization switching. We find that compared to an isolated nanomagnet under similar illumination conditions, localized surface plasmon resonances in the coupled system generate larger magnetic fields in the nanomagnets.

Bradlee Beauchamp

Papers

Surface-plasmon Opto-magnetic Field Enhancement for All-optical Magnetization Switching

Hybrid magneto photonic material structure for plasmon assisted magnetic switching

Temperature-dependent magnetic transitions in CoCrPt-Ru-CoCrPt synthetic ferrimagnets

Hybrid Magneto Photonic Material Structure for Plasmon Assisted Magnetic Switching

Surface-plasmon opto-magnetic field enhancement for magnetization reversal of on-chip nanomagnets