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1. Ultrastrong magnon-magnon coupling and chiral spin-texture control in a dipolar 3D multilayered artificial spin-vortex ice

   https://doi.org/10.1038/s41467-024-48080-z  

   Dion, Troy; Stenning, Kilian D.; Vanstone, Alex; Holder, Holly H.; Sultana, Rawnak; Alatteili, Ghanem; Martinez, Victoria; Kaffash, Mojtaba Taghipour; Kimura, Takashi; Oulton, Rupert F.; et al (May 2024, Nature Communications)

   Strongly-interacting nanomagnetic arrays are ideal systems for exploring reconfigurable magnonics. They provide huge microstate spaces and integrated solutions for storage and neuromorphic computing alongside GHz functionality. These systems may be broadly assessed by their range of reliably accessible states and the strength of magnon coupling phenomena and nonlinearities. Increasingly, nanomagnetic systems are expanding into three-dimensional architectures. This has enhanced the range of available magnetic microstates and functional behaviours, but engineering control over 3D states and dynamics remains challenging. Here, we introduce a 3D magnonic metamaterial composed from multilayered artificial spin ice nanoarrays. Comprising two magnetic layers separated by a non-magnetic spacer, each nanoisland may assume four macrospin or vortex states per magnetic layer. This creates a system with a rich 16^Nmicrostate space and intense static and dynamic dipolar magnetic coupling. The system exhibits a broad range of emergent phenomena driven by the strong inter-layer dipolar interaction, including ultrastrong magnon-magnon coupling with normalised coupling rates of$$\frac{\Delta f}{\nu }=0.57$$ $\frac{\Delta f}{\nu }=0.57$, GHz mode shifts in zero applied field and chirality-control of magnetic vortex microstates with corresponding magnonic spectra. 

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2. Spin disorder control of topological spin texture

   https://doi.org/10.1038/s41467-024-47715-5  

   Zhang, Hongrui; Shao, Yu-Tsun; Chen, Xiang; Zhang, Binhua; Wang, Tianye; Meng, Fanhao; Xu, Kun; Meisenheimer, Peter; Chen, Xianzhe; Huang, Xiaoxi; et al (December 2024, Nature Communications)

   Abstract Stabilization of topological spin textures in layered magnets has the potential to drive the development of advanced low-dimensional spintronics devices. However, achieving reliable and flexible manipulation of the topological spin textures beyond skyrmion in a two-dimensional magnet system remains challenging. Here, we demonstrate the introduction of magnetic iron atoms between the van der Waals gap of a layered magnet, Fe₃GaTe₂, to modify local anisotropic magnetic interactions. Consequently, we present direct observations of the order-disorder skyrmion lattices transition. In addition, non-trivial topological solitons, such as skyrmioniums and skyrmion bags, are realized at room temperature. Our work highlights the influence of random spin control of non-trivial topological spin textures. 

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3. 2024 roadmap on magnetic microscopy techniques and their applications in materials science

   https://doi.org/10.1088/2515-7639/ad31b5  

   Christensen, D V; Staub, U; Devidas, T R; Kalisky, B; Nowack, K C; Webb, J L; Andersen, U L; Huck, A; Broadway, D A; Wagner, K; et al (June 2024, Journal of Physics: Materials)

   Abstract Considering the growing interest in magnetic materials for unconventional computing, data storage, and sensor applications, there is active research not only on material synthesis but also characterisation of their properties. In addition to structural and integral magnetic characterisations, imaging of magnetisation patterns, current distributions and magnetic fields at nano- and microscale is of major importance to understand the material responses and qualify them for specific applications. In this roadmap, we aim to cover a broad portfolio of techniques to perform nano- and microscale magnetic imaging using superconducting quantum interference devices, spin centre and Hall effect magnetometries, scanning probe microscopies, x-ray- and electron-based methods as well as magnetooptics and nanoscale magnetic resonance imaging. The roadmap is aimed as a single access point of information for experts in the field as well as the young generation of students outlining prospects of the development of magnetic imaging technologies for the upcoming decade with a focus on physics, materials science, and chemistry of planar, three-dimensional and geometrically curved objects of different material classes including two-dimensional materials, complex oxides, semi-metals, multiferroics, skyrmions, antiferromagnets, frustrated magnets, magnetic molecules/nanoparticles, ionic conductors, superconductors, spintronic and spinorbitronic materials. 

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4. Unified topological characterization of electronic states in spin textures from noncommutative $K$ -theory

   https://doi.org/10.1103/PhysRevResearch.6.013102  

   Lux, Fabian R; Ghosh, Sumit; Prass, Pascal; Prodan, Emil; Mokrousov, Yuriy (January 2024, Physical Review Research)

   The nontrivial topology of spin systems such as skyrmions in real space can promote complex electronic states. Here, we provide a general viewpoint at the emergence of topological spectral gaps in spin systems based on the methods of noncommutative $K$-theory. By realizing that the structure of the observable algebra of spin textures is determined by the algebraic properties of the noncommutative torus, we arrive at a unified understanding of topological electronic states which we predict to arise in various noncollinear setups. The power of our approach lies in an ability to categorize emergent topological states algebraically without referring to smooth real- or reciprocal-space quantities. This opens a way towards an educated design of topological phases in aperiodic, disordered, or nonsmooth textures of spins and charges containing topological defects. Published by the American Physical Society2024 

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5. Topological insulators for efficient spin–orbit torques

   https://doi.org/10.1063/5.0048619  

   Han, Jiahao; Liu, Luqiao (May 2021, APL Materials)

   Current-induced magnetic switching via spin–orbit torques has been extensively pursued for memory and logic applications with promising energy efficiency. Topological insulators are a group of materials with spin-momentum locked electronic states at the surface due to spin–orbit coupling, which can be harnessed to reach strong spin–orbit torques. In this paper, we summarize and compare the methods for calibrating the charge-spin conversion efficiency in topological insulators, with which topological insulators are identified as outstanding spin–orbit torque generators compared with the well-studied heavy metals. We then review the results of magnetic switching under reduced current density in topological insulator/ferromagnet heterostructures. Finally, we provide insights on current challenges as well as possible exploration directions in the emerging field of topological spintronics. 

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