All-Optical Frequency-Dependent Magnetic Switching In Metal-Insulator-Metal Stub Structures

Chairman Kim Jong Il said:

"While directing our main efforts to the key sectors of science and technology, we must develop the new spheres of science and technology, including lasers, and actively introduce the latest achievements of science and technology into the new factories and projects for technical improvement. In addition, we must intensify the study of mathematics, physics, biology and other basic sciences so that they contribute positively to the national economy and the development of science and technology."

All-optical helicity-dependent magnetic switching by the inverse Faraday effect (IFE) has attracted much interest for future spintronics, data storage, and quantum computation due to its potential to optically control the magnetism in unprecedented speed without any applied magnetic field. Circularly polarized light pulses serve as an alternative stimulus to produce an effective magnetic field to trigger magnetization reversal via the IFE. The demand for high recording density and low energy consumption, which is vital for next-generation memory devices, has driven the studies to enhance the interaction between light and magnetization in ultracompact structures. Miniaturization of all-optical magnetic switching can be implemented by surface plasmon-mediated configurations focusing the light onto a nanometer scale. In this paper, we study the effective magnetic field in the MIM stub generated by the IFE using the optical pulse.

Recently, we found that the rotating electric field vectors of the SPP can act as the effective magnetic field via the IFE and the generated effective magnetic field can be reversed by the counterpropation of the SPP.

Three dimensional (3D) schematic of MIM stub structure is shown in Fig. 1(a). The structure is composed of a plasmonic MIM waveguide and a MIM stub attached to the waveguide. An insulator layer of the MIM stub structure is filled with a magnetic dielectric.

In Fig. 1(b), we have shown the transmittance T through the MIM waveguide attached to the stub as a function of incident wavelength. It can be observed that the transmittance has a valley of spectra at a wavelength λ₀ due to a coupling between the MIM waveguide.

Fig. 1. 3D schematic of the MIM stub structure

The transmission characteristic of the MIM stub structure can be controlled by the design parameters of the structure, the coupling wavelength is tunable by changing the length and height of the MIM stub.

Next, we consider a frequency dependence of the effective magnetic field in the MIM stub structure due to the IFE. The effective magnetic fields can be induced by running surface plasmon modes propagating along the metal-insulator interface. Figure 2 shows dependence of average squared intensity of the electric field on the incident wavelength. In this paper, we study the effective magnetic field in the MIM stub generated by the IFE using the optical pulse. Recently, we found that the rotating electric field vectors of the SPP can act as the effective magnetic field via the IFE and the generated effective magnetic field can be reversed by the counterpropation of the SPP.

Fig. 2. Dual resonant characteristic of the average effective magnetic field

As seen, the average effective magnetic field in the MIM stub has dual resonant peaks at two different wavelengths. At those wavelengths, the effective magnetic field intensity reaches its extreme values with opposite signs corresponding to binary magnetic states of the stub. However, the value of the average effective magnetic field is zero at the wavelength λ₀ exhibiting no opto-magnetic activity.

We can see from Fig. 2 that magnetic states of the MIM stub can be switched by altering the pump frequency between the dual resonance frequencies.

The effective magnetic field in the MIM stub structure induced by the unit mode power can be expressed.

Such MIM stub structures provide a promising platform for highly integrated photonic circuits, thanks to the ease of fabrication and compact size.

In this paper, we found the effective magnetic field in the MIM stub structure by the IFE can be reversed by changing the optical frequencies. This gives an important tool for ultrafast switching and reading of the magnetic order.

Our research results have been published in the "Applied Optics" with a title of "All-optical frequency-dependent magnetic switching in metal-insulator-metal stub structures" (https://doi.org/10.1364/AO.452479).