ABSTRACT
Magnetic memory combining plasmonics and magnetism is poised to dramatically increase the bit density and energy efficiency of light-assisted ultrafast magnetic storage, thanks to nanoplasmon-driven enhancement and confinement of light. Here we devise a new path for that, simultaneously enabling light-driven bit downscaling, reduction of the required energy for magnetic memory writing, and a subtle control over the degree of demagnetization in a magnetophotonic surface crystal. It features a regular array of truncated-nanocone-shaped Au-TbCo antennas showing both localized plasmon and surface lattice resonance modes. The ultrafast magnetization dynamics of the nanoantennas show a 3-fold resonant enhancement of the demagnetization efficiency. The degree of demagnetization is further tuned by activating surface lattice modes. This reveals a platform where ultrafast demagnetization is localized at the nanoscale and its extent can be controlled at will, rendering it multistate and potentially opening up so-far-unforeseen nanomagnetic neuromorphic-like systems operating at femtosecond time scales controlled by light.
ABSTRACT
The pyrochlore iridates (Eu1-xBix)2Ir2O7(0⩽x⩽1) undergo an anomalous negative lattice expansion for small Bi-doping (x⩽0.035) (region I) and a normal lattice expansion forx⩾0.1(region II); this is accompanied by a transition from an insulating (and magnetically ordered) to a metallic (and with no magnetic ordering) ground state. Here, we investigate (Eu1-xBix)2Ir2O7(0⩽x⩽1) using hard x-ray photoemission spectroscopy and x-ray absorption fine structure (XAFS) spectroscopy. By analyzing the Eu-L3, Ir-L3and Bi-L2&L3edges x-ray absorption near edge structure spectra and Eu-3dcore-level XPS spectra, we show that the metal cations retain their nominal valence, namely, Ir4+, Bi3+and Eu3+, respectively, throughout the series. The Ir-4fand Bi-4fcore-level XPS spectra consist of screened and unscreened doublets. The unscreened component is dominant In the insulating range (x⩽0.035), and in the metallic region (x⩾0.1), the screened component dominates the spectra. The Eu-3dcore-level spectra remain invariant under Bi doping. The extended XAFS data show that the coordination around the Ir remains well preserved throughout the series. The evolution of the valence band spectra near the Fermi energy with increasing Bi doping indicates the presence of strong Ir(5d)-Bi(6p) hybridization which drives the metal-to-insulator transition.
ABSTRACT
The quest to improve the density, speed and energy efficiency of magnetic memory storage has led to the exploration of new ways of optically manipulating magnetism at the ultrafast time scale, in particular in ferrimagnetic alloys. While all-optical magnetization switching is well-established on the femtosecond timescale, lateral nanoscale confinement and thus the potential significant reduction of the size of the magnetic element remains an outstanding challenge. Here we employ resonant electromagnetic energy funneling through plasmon nanoantennas to influence the demagnetization dynamics of a ferrimagnetic TbCo alloy thin film. We demonstrate how Ag nanoring-shaped antennas under resonant optical femtosecond pumping reduce the overall demagnetization in the underlying films up to three times compared to non-resonant illumination. We attribute such a substantial reduction to the nanoscale confinement of the demagnetization process. This is qualitatively supported by the electromagnetic simulations that strongly evidence the resonant optical energy-funneling to the nanoscale from the nanoantennas into the ferrimagnetic film. This observation is an important step for reaching deterministic ultrafast all-optical magnetization switching at the nanoscale in such systems, opening a route to develop nanoscale ultrafast magneto-optics.
