Ultra-fast plasmon-enhanced magnetic bit switching at the nanoscale

Researchers at the Max Born Institute have demonstrated a successful method for controlling and manipulating nanoscale magnetic bits (components of digital data) using ultrafast laser pulses and plasmonic gold nanostructures. The findings have been published on Nano Letters.

All-optic, helicity-independent magnetization switching (AO-HIS) is one of the most interesting and promising mechanisms of this effort, allowing the magnetization state to reverse between two directions with a single femtosecond laser pulse, allowing “0” and “1S” to work without external magnetic fields or complex wiring. This opens up exciting possibilities for creating memory devices that are not only faster and more robust, but also consume much less power.

Ultra-fast optical drive control of magnetization at nanometer-length scales is key to achieving competitive bit sizes with next-generation data storage technologies. However, there is currently not a good understanding of the extent to which basic physics processes such as nanoscale and magnetic domain wall propagation minimize achievable bit sizes.

To investigate these unresolved questions, the researchers used plasmonic gold nanostructures. This allows light to be trapped in an area smaller than the wavelength of the light. These structures are manufactured in-house by electron beam lithography on 10 nm thin films of magnetic materials made of rare earth metal alloys (GDTBCO), and the presence of rare earth metal terbium promotes small, stable magnetic domains and allows for the production of large magnetic dissectants.

Magnetic switching was achieved at a width of 240 nm using a 370 FS ultra-short laser pulse with a 1030 nm wavelength. The nanostructures also reduced the required pulse energy to enhance the localization of the electromagnetic field around the gold bar and exploit the plasmonic properties.

Illumination with a single laser pulse can be used to locally switch magnetization at the edges of nanostructures. Additionally, the area of ​​magnetization switched by the laser pulse can be returned with another single laser pulse at the precise targeted position of the magnetic material.

Therefore, it is possible to achieve controlled switching of magnetization required to encode information. The final magnetic state was visualized using Magnetic Force Microscopy (MFM), a scanning technique that allows the imaging of the magnetic state of a sample with nanometer-scale spatial resolution.

In addition to demonstrating toggle switching under specific laser pulse conditions, researchers observed interesting extended magnetization patterns. When nanostructures are exciting under conditions that do not allow plasmon resonance to be excited by lasers, distant magnetic field scattering domain patterns, such as dipole, are “engraved” on the magnetic film. The domination of various plasmonic energy transfer mechanisms was possible via on and off resonance plasmonic excitations.

“This is a fundamental study of the basic process of local optical switching of magnetization, but it can guide future developments towards optimized excitation schemes for designed magnetic materials, and ultimately utilize the nanoscale control of magnetism using light. Research.