Scientists demonstrated that patterning magnetic material into arrays of nanoscale dots allows for a strong and controllable modification of the polarization of light.
The recent breakthrough could help improve the sensitivity of optical components of telecommunication and biosensing devices, Aalto University reported.
The partnership between light and magnetization in ferromagnetic materials is based on quantum mechanical interactions that result in magneto-optical effects, which have an influence of properties such as polarization axis or light intensity. The interactions of light and matter are enhanced at the nanoscale. Nano-sized metallic nanoparticles can be looked at as antennae for visible wavelengths; this new research turned to a phenomenon called surface lattice resonances, in which the nanoparticles radiate together in an array. This arrangement is created through the assembly of magnetic nanoantennas on a length scale that match the wavelength of incoming light.
The strong interactions between the nanoparticles create collective oscillations, a behavior that has been previously seen noble metal nanoparticles. This new research shows the same phenomenon can be seen in magnetic materials, and the surface lattice resonances boost light polarization change in ferromagnetic materials in what is called the "magneto-optical Kerr effect."
"A key finding of our research was that the frequency, that is the [color] of light, for which this happens can be made different from the frequency where the purely optical effect is strongest. The separation of magneto-optical and optical signals was achieved by choosing a different distance between the nanoparticles in the two directions of the array," said Prof. Päivi Törmä.
In the past, optical activity in ferromagnetic materials was limited to high resistance, making it almost impossible to observe plasmon resonances in noble metals.
"However, by ordering the nanoparticles in arrays and taking advantage of collective resonances, this problem was mitigated. Or result opens an important new direction in the research field that focuses on the coupling of light and magnetization at the nanoscale," said Prof. Sebastiaan van Dijken.
The findings were published in a recent edition of the journal Nature Communications.
