Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session G68: Ultrafast Magnetization DynamicsInvited
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Sponsoring Units: GMAG Chair: Olle Eriksson, Uppsala University Room: Room 420 |
Tuesday, March 7, 2023 11:30AM - 12:06PM |
G68.00001: Imaging ultrafast and ultrasmall: Capturing ultrafast magnetization using fs x-rays Invited Speaker: Roopali Kukreja Ultrafast control of magnetization with light holds the promise of being a new paradigm for the next generation memory and data storage devices. There is an explosive increase in studies that aim to understand the mechanisms of photon-driven spin dynamics at such short time-scales. However, it has been recently recognized that spatial domain pattern and nanoscale heterogeneities can play a critical role in dictating the ultrafast behavior [1-5]. These and many other experimental findings in ultrafast spin dynamics are now possible due to emerging coherent x-ray/EUV sources that combine the power of x-rays with fs time resolution [6]. I will highlight some of the intriguing data obtained in the recent years with x-ray/EUV free electron lasers (FELs) that hint at the rich variety of magnetic behavior at the frontier of the ultrafast and ultra-small. I will focus on some of our recent results obtained at the European XFEL and FERMI that demonstrate how spin textures are spatially perturbed under ultrafast optical pumping conditions. Surprisingly, we found that the spatial symmetry of spin textures affects ultrafast spatial dynamics at the nm length scale [7,8]. Specifically, we observe nontrivial distortions in the shape of magnetic diffraction patterns depending on the symmetry of the magnetic domain pattern. In addition, these distortions are distinctly nonlinear in pump fluence with a threshold, reminiscent of the threshold behavior for driven domain wall motion. Our results settle the debate as to whether ultrafast optical pumping instigates domain dynamics, and show that the dynamics depend strongly on both the details of the domain pattern and the pump energy. While the evidence supporting ultrafast domain dynamics is now substantial, the mechanism (or mechanisms) underlying these effects is not yet clear. Superdiffusive spin currents [9] have been proposed as one possible explanation [4,5]. Regardless, these intriguing observations suggest that texture-dependent ultrafast spin transport might provide us with novel ways to manipulate spin degrees of freedom. |
Tuesday, March 7, 2023 12:06PM - 12:42PM |
G68.00002: Nanoscale ultrafast magnetization behavior: from solitons to domain-wall displacement Invited Speaker: Ezio Iacocca Ultrafast magnetization switching has made it possible to envision new techniques for information storage at sub-nanosecond timescales. By switching, it is typically understood that a large spatial region of the magnetic material reverses its orientation, traditionally detected by spatially averaged measurements such as x-ray magnetic circular dichroism. However, access to time-dependent scattered x-rays revealed richer dynamics occurring at the nanoscale. In this talk, I will discuss advances in the analysis of x-ray scattering data to uncover nucleation of solitons and ultrafast domain perturbations. These dynamics entail both atomic and long-range interactions that represent a formidable yet interesting multiscale modeling problem. A new pseudo-spectral magnetization dynamics model provides promising results that could hold the key to achieving seamless multiscaling between atomistic spin dynamics and micromagnetic simulations. |
Tuesday, March 7, 2023 12:42PM - 1:18PM |
G68.00003: Ultrafast magnetic switching induced by picosecond electric current pulses Invited Speaker: Jeffrey Bokor The field of spintronics involves the study of both spin and charge transport in solid-state devices. Ultrafast magnetism involves the use of femtosecond laser pulses to manipulate magnetic order on subpicosecond time scales, including helicity-independent all-optical switching. We have united these phenomena by using picosecond charge current pulses generated on-chip using an ultrafast photoconducting (Auston) switch to induce deterministic, repeatable ultrafast reversal of the magnetization of a ferromagnetic GdFeCo thin film. Using 9 ps duration current pulses, the magnetization reverses in ~10 ps, which is more than one order of magnitude faster than any other electrically controlled magnetic switching, and demonstrates a fundamentally new electrical switching mechanism that does not require spin-polarized currents or spin-transfer/orbit torques. Furthermore, the energy density required for switching is low, projecting to only 4 fJ needed to switch a (20 nm)3 cell. |
Tuesday, March 7, 2023 1:18PM - 1:54PM |
G68.00004: Ultrafast coherent nonlinear magnonics in antiferromagnets Invited Speaker: Davide Bossini The wildly growing field of antiferromagnetic spintronics is currently addressing several fundamental questions. A major topic of investigations concerns the possibility to drive and manipulate coherent magnons on the ultrafast timescale. The proposition that driving such magnon modes, in a strongly nonlinear regime, could even result in switching coherently the order parameter on the femtosecond timescale needs to be considered. In my talk, I will discuss two approaches to nonlinear regime of coherent magnon dynamics. |
Tuesday, March 7, 2023 1:54PM - 2:30PM |
G68.00005: Role of polarized phonons during ultrafast demagnetization Invited Speaker: Ulrich Nowak The transfer and control of angular momentum is a key aspect for spintronic applications. When a thin nickel film is subjected to ultrashort laser pulses, it can lose its magnetic order almost completely within merely femtosecond times. This phenomenon offers opportunities for rapid information processing or ultrafast spintronics. Consequently, ultrafast demagnetization is central to modern material research, but a crucial question has remained elusive: If a material loses its magnetization within only femtoseconds, where is the missing angular momentum on such short time scales? |
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