Nickel nanoparticle arrays enhance the efficiency of plasmon magnetization devices

The ability to reverse magnetization in ferromagnetic materials with femtosecond laser pulses has opened new doors for ultrafast magnetic data storage. Much work still remains, however, in confining optically induced magnetic switching events to the nanoscale and improving these devices’ efficiency. Reporting their work in Applied Physics Letters, researchers demonstrated a new technique that leverages plasmon resonances in nickel nanostructure arrays to increase the effect light has on a material’s magnetic properties.

The system used femtosecond laser pulses to stimulate nickel nanodiscs at different wavelengths, ranging from 610 to 700 nanometers in 10 nanometer intervals. A dark-field magneto-optical microscope measured the magnetization changes following illumination by the pulses. When ordered into an optimally spaced array for the laser’s wavelength, interactions between localized plasmon resonances in the nickel nanodiscs produced an intense surface lattice resonance (SLR).

The authors found that the excitation of this collective plasmon mode produced stronger magnetic effects, including full demagnetization and magnetic switching in a small magnetic bias field. The excitation of the SLR mode caused more efficient heating of the nanoparticles to their Curie temperature, at which point the array’s magnetic properties could be altered. Tuned samples required a beam intensity roughly one-third the energy the material needed when not in resonance to fully randomize the magnetization of the nanoparticles in the center of the laser spot. Thermo-plasmonic models strongly agreed with the experimental data.

The group did not find conclusive evidence for all-optical magnetic switching, as linearly and circularly polarized laser pulses yielded the same results. Next, the team plans to investigate the possibility of inducing magnetic switching effects by using purely optical means.

Source: “Plasmon-induced demagnetization and magnetic switching in nickel nanoparticle arrays,” by Mikko Kataja, Francisco Freire-Fernández, Jorn P. Witteveen, Tommi Hakala, Päivi Törmä, and Sebastiaan van Dijken, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5012857 .