Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session G29: Towards Skyrmionics Manipulating Spin Textures in MagnetsInvited Live Streamed
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Sponsoring Units: GMAG DCMP DMP FIAP Chair: Vincent Cros, CNRS/Thales, France Room: McCormick Place W-190B |
Tuesday, March 15, 2022 11:30AM - 12:06PM |
G29.00001: Computing with Magnetic Skyrmions Invited Speaker: Avik W Ghosh Solitonic magnetic excitations such as skyrmions embody the promise of potentially compact, high density, ultrafast, all-electronic, low-energy devices. I will discuss skyrmionics in the context of the overall solid-state memory landscape and show how their size, stability, and mobility can be controlled by material engineering of saturation magnetization in nearly compensated ferrimagnets, damping in Heuslers and Dzyaloshinskii-Moriya in alloyed heavy metal under-layers with d-orbital alignment [1]. Furthermore, geometrical parameters such as film thickness, defect density, and notches can be used to tune skyrmion properties, such as their size, stability and lifetime. Successful engineering of individual skyrmions - in effect, small mobile magnets, can usher in unique applications such as temporal state machines, capitalizing on their near ballistic current-velocity relation to map temporal data to spatial data without any intervening domain conversion costs. |
Tuesday, March 15, 2022 12:06PM - 12:42PM |
G29.00002: Skyrmion device integration – deterministic and ultrafast creation, annihilation, and propagation Invited Speaker: Felix Buettner Magnetic skyrmions have many promising applications, from sensors through data storage to non-conventional computing. Almost all applications rely on deterministic control of the skyrmion behavior. Of particular importance is control over the skyrmion creation, their annihilation, and their propagation processes. Moreover, in most cases, it is paramount that these operations are completed on a pico- to low-nanosecond timescale. Here, I will discuss various means to achieve such deterministic and ultrafast control over the skyrmion behavior via electrical and optical stimuli and via global and local tuning of the materials’ properties. I will discuss the underlying mechanisms of switching, how they differ between electrical and optical excitations, and how this can be exploited to achieve new functionality in opto-spintronic devices. I will also discuss various means of driving skyrmions into motion and comment on the maximum velocity that can be achieved. I will conclude with an outlook on remaining challenges that need to be addressed before skyrmions will become actually useful for commercial device applications.
Outreach-highlight: Magnetic skyrmions have many promising applications, from sensors through data storage to non-conventional computing. This presentation will focus on how the basic operating principles of such applications, namely the nucleation, annihilation, and propagation of magnetic skyrmions, can be achieved at a technologically relevant speed (sub-nanoseconds) and with technologically required reliability. |
Tuesday, March 15, 2022 12:42PM - 1:18PM |
G29.00003: Atomic-scale visualization and manipulation of topological spin textures in the chiral magnet, MnGe Invited Speaker: Jay Gupta Topological spin textures in chiral magnets are of fundamental interest and may enable novel magnetic storage and computing technologies. In MnGe, such textures arise from the competition of ferromagnetic exchange, favoring aligned spins, and the Dzyaloshinskii-Moriya interaction (DMI) which favors perpendicular spins. In our spin-polarized STM studies of MnGe thin films, we study spin textures at the surface, where DMI may arise not only from the non-centrosymmetric 'B20' MnGe crystal structure, but also from the surface itself. Furthermore, the thin film structures allow us to study strain effects, and provide a path for integration into heterostructures. Our SP-STM images indicate helical stripe domains with a 6 nm period, which micromagnetic modeling helps us understand as a surface projection of the helical wavevector, which is canted away from the film normal. We can deduce the three-dimensional orientation of the helical wavevectors at domain walls, and we predict that three helical domains can meet in two distinct ways to produce either a 'target-like' or a 'π-like' topological spin texture. Both textures are observed experimentally, and are found in strained regions of the films. Topological defects in the target texture can be created, moved and annihilated with current/voltage pulsing from the STM tip. The core of the target texture itself can be similarly moved, and can also be reversibly switched with applied magnetic field. These studies represent an initial step toward understanding the interplay of bulk and surface magnetism in chiral magnets, and the manipulation of these topological spin textures is a promising step toward future spintronics applications. |
Tuesday, March 15, 2022 1:18PM - 1:54PM |
G29.00004: Non-collinear three-dimensional textures in magnetic multilayers: Hatching of skyrmionic cocoons Invited Speaker: Nicolas Reyren Two-dimensional magnetic textures such as skyrmions or chiral domain walls were mostly under focus for the last decade, but recently interest has surged for more complex objects which display an inhomogeneous behavior over the vertical dimension. Interesting examples include bobbers which could become remarkable assets for the development of logic devices [1] or the recently observed hopfions [2] or even different skyrmions phases[3]. In this study, we engineer and explore three-dimensional textures allowed us to observe the signature of potential new textures, which we will name skyrmionic cocoons. At low magnetic field, they resemble tubular skyrmions but upon an increase of the out-of-plane field, they shrink and disappear in the outer layers becoming elongated ellipsoids. By carefully tuning the thickness of each magnetic layer, it is possible to observe in a single sample two distinct objects, as shown by the strong difference in the Magnetic Force Microscopy (MFM) contrasts. With the support of micromagnetic simulations, we identify them as two vertically coupled cocoons (large contrast) and single cocoons only present in half of the layers (weak contrast). The existence and field-dependent behavior of such textures could represent interesting possibilities for potential applications. |
Tuesday, March 15, 2022 1:54PM - 2:30PM |
G29.00005: Skyrmion Lattices as Context-Aware Artificial Neurons Invited Speaker: Jean A Incorvia Magnetic skyrmions offer a rich physical space for hardware-aware computing, including making use of skyrmion core oscillations and skyrmion-skyrmion interactions. The behavior of arrays of skyrmions can be manipulated by multiple inputs, such as currents and electromagnetic waves. Charge current reconfigures the skyrmion lattice, thereby modulating the neuron's state, its dynamics, and its transfer function. We will show in simulation that the skyrmion lattice can therefore mimic essential advanced functionalities of the brain for adaptive intelligence, namely context-awareness, cross-frequency coupling, and feature binding. We use the skyrmion neuron to construct an adaptive artificial neural network (ANN) and show that it can perform context-aware diagnosis of breast cancer, with higher accuracy while learning faster from smaller amounts of data and using a more compact and energy-efficient network than the state-of-the-art non-adaptive ANNs used for cancer diagnosis. This work describes how hardware-based adaptive neurons can mitigate several critical challenges facing contemporary ANNs. Modern ANNs require large amounts of training data, energy and chip area and are highly task-specific. Conversely, hardware-based ANNs built with adaptive neurons show faster learning from smaller datasets, compact architectures, energy-efficiency, fault-tolerance, and can lead to the realization of general artificial intelligence. |
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