a) intensity of diffraction of first and b) second order as a function of the delay between the beams of the pump and the probe. c) Intensity ratio between second and first diffraction order (R21) as a function of excitation flux with a delay of 50 ps. With a flux of 1.3 arb.u., the transient magnetization network begins to change shape giving rise to the appearance of the second order of diffraction, a fingerprint for AOS. d) The R21 ratio for a high excitation flux (red circles) has a large and constant ratio, which we identify as the appearance of stable magnetic structures and, therefore, as additional evidence of AOS on a spatial scale. nanometers. Credit: Max Born Institute
Ultra-fast control of nanoscale light-driven magnetization is key to achieving competitive bit sizes in next-generation data storage technology. Researchers at the Max Born Institute in Berlin and the large-scale Elettra facility in Trieste, Italy, have successfully demonstrated the ultra-rapid emergence of fully optical switching by generating a nanoscale network by two-pulse interference in the range. extreme ultraviolet spectral.
The physics of optically driven magnetization dynamics on the femtosecond time scale is of great interest for two main reasons: first, for a deeper understanding of the fundamental mechanisms of non-equilibrium, ultrafast spin dynamics, and second, for to the potential application in the next generation of information technology with the vision of meeting the need for faster and more energy efficient data storage devices.
Fully Optical Switching (AOS) is one of the most interesting and promising mechanisms for this effort, where the state of magnetization can be reversed between two directions with a single femtosecond laser pulse, which serves as “0s” and “1s “. While the understanding of AOS time control has progressed rapidly, knowledge about nanometer-scale ultrafast transport phenomena, important for the realization of fully optical magnetic inversion in technological applications, has remained limited due to the wavelength limitations of optical radiation. An elegant way to overcome these constraints is to reduce the wavelengths to the extreme ultraviolet (XUV) spectral range in transient grid experiments. This technique is based on the interference of two XUV beams leading to a nanoscale excitation pattern and has pioneered the EIS-Timer line of the FERMI Free Electron Laser (FEL) light in Trieste, Italy.
Researchers at the Max-Born-Institute in Berlin and the FEL FERMI facility have now excited a transient magnetic grid (TMG) with a periodicity of ΛTMG = 87 nm in a sample of ferrimagnetic GdFe alloy. The spatial evolution of the magnetization network was probed by the diffraction of a time-delayed third XUV pulse tuned to the N edge of Gd at a wavelength of 8.3 nm (150 eV). Because the AOS exhibits a strongly nonlinear response to excitation, changes in symmetry characteristic of the evolving magnetic grid other than the initial sinusoidal excitation pattern are expected. This information is encoded directly in the diffraction pattern: in the case of a linear magnetization response to excitation and without AOS, a sinusoidal TMG is induced and the second order of diffraction is suppressed. However, if AOS occurs, the shape of the lattice changes, now allowing a pronounced second-order diffraction intensity. In other words, the researchers identified the intensity ratio between the second and first order (R21) as an observable fingerprint for AOS in diffraction experiments.
In the image above, a) and b) show the temporal evolution of the first and second order diffracted intensities, respectively. The researchers found comparable decay times of τRE, first = (81 ± 7) ps and τRE, second = (90 ± 24) ps, according to the lateral heat diffusion rates of the nanoscale grids. c), shows the ratio R21 as a function of the excitation flux with a constant delay of the pump probe of 50 ps. For a low creep below the AOS threshold, the research team observed a steady, small value of R21 around 1%. Increased excitation, however, R21 shows a steady increase to 88%, providing the first evidence of AOS on the nanoscale length scale. The R21 ratio as a function of time is shown ad) for two selected excitation currents. For the largest creep (red circles) R21 has a high and constant proportion of approximately 6% during the measured time interval of 150 ps, indicative of a stable magnetic structure, which is interpreted as optically inverted domains, i.e. AOS. Finally, the researchers were able to confirm their observations using fully optical complementary measurements in real space using time-resolved Faraday microscopy.
In future experiments of transient grids with significantly smaller periodicities up to
The research was published in Nano letters.
Information on the rapid appearance of magnetization More information: Kelvin Yao et al, All-Optical Switching on the Nanometer Scale Excited and Probed with Femtosegon Extreme Ultraviolet Pulses, Nano letters (2022). DOI: 10.1021 / acs.nanolett.2c01060
Taught by Max Born Institute
Citation: Fully Optical Nanoscale Switching (2022, June 15) Retrieved June 15, 2022
This document is subject to copyright. Apart from any fair treatment for private study or research purposes, no part may be reproduced without the written permission. Content is provided for informational purposes only.