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1. Tailoring magnon modes by extending square, kagome, and trigonal spin ice lattices vertically via interlayer coupling of trilayer nanomagnets

   https://doi.org/10.1088/1361-648X/ad5d3f  

   de_Rojas, Julius; Atkinson, Del; Adeyeye, Adekunle O (July 2024, Journal of Physics: Condensed Matter)

   Abstract In this work high-frequency magnetization dynamics and statics of artificial spin-ice lattices with different geometric nanostructure array configurations are studied where the individual nanostructures are composed of ferromagnetic/non-magnetic/ferromagnetic trilayers with different non-magnetic thicknesses. These thickness variations enable additional control over the magnetic interactions within the spin-ice lattice that directly impacts the resulting magnetization dynamics and the associated magnonic modes. Specifically the geometric arrangements studied are square, kagome and trigonal spin ice configurations, where the individual lithographically patterned nanomagnets (NMs) are trilayers, made up of two magnetic layers of ${\text{Ni}}_{81}{\text{Fe}}_{19}$of 30 nm and 70 nm thickness respectively, separated by a non-magnetic copper layer of either 2 nm or 40 nm. We show that coupling via the magnetostatic interactions between the ferromagnetic layers of the NMs within square, kagome and trigonal spin-ice lattices offers fine-control over magnetization states and magnetic resonant modes. In particular, the kagome and trigonal lattices allow tuning of an additional mode and the spacing between multiple resonance modes, increasing functionality beyond square lattices. These results demonstrate the ability to move beyond quasi-2D single magnetic layer nanomagnetics via control of the vertical interlayer interactions in spin ice arrays. This additional control enables multi-mode magnonic programmability of the resonance spectra, which has potential for magnetic metamaterials for microwave or information processing applications. 

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2. Matrix product study of spin fractionalization in the one-dimensional Kondo insulator

   https://doi.org/10.1103/PhysRevResearch.6.023227  

   Chen, Jing; Stoudenmire, E Miles; Komijani, Yashar; Coleman, Piers (June 2024, Physical Review Research)

   The Kondo lattice is one of the classic examples of strongly correlated electronic systems. We conduct a controlled study of the Kondo lattice in one dimension, highlighting the role of excitations created by the composite fermion operator. Using time-dependent matrix product state methods, we compute various correlation functions and contrast them with both large-N mean-field theory and the strong-coupling expansion. We show that the composite fermion operator creates long-lived, charge-e and spin-1/2 excitations, which cover the low-lying single-particle excitation spectrum of the system. Furthermore, spin excitations can be thought to be composed of such fractionalized quasiparticles with a residual interaction which tend to disappear at weak Kondo coupling. Published by the American Physical Society2024 

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3. String Phase in an Artificial Spin Ice

   https://doi.org/10.1038/s41467-021-26734-6  

   Zhang, Xiaoyu; Duzgun, Ayhan; Lao, Yuyang; Subzwari, Shayaan; Bingham, Nicholas S.; Sklenar, Joseph; Saglam, Hilal; Ramberger, Justin; Batley, Joseph T.; Watts, Justin D.; et al (December 2021, Nature Communications)

   Abstract One-dimensional strings of local excitations are a fascinating feature of the physical behavior of strongly correlated topological quantum matter. Here we study strings of local excitations in a classical system of interacting nanomagnets, the Santa Fe Ice geometry of artificial spin ice. We measured the moment configuration of the nanomagnets, both after annealing near the ferromagnetic Curie point and in a thermally dynamic state. While the Santa Fe Ice lattice structure is complex, we demonstrate that its disordered magnetic state is naturally described within a framework of emergent strings. We show experimentally that the string length follows a simple Boltzmann distribution with an energy scale that is associated with the system’s magnetic interactions and is consistent with theoretical predictions. The results demonstrate that string descriptions and associated topological characteristics are not unique to quantum models but can also provide a simplifying description of complex classical systems with non-trivial frustration. 

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4. Ice sculpting: An artificial spin ice Tutorial on controlling microstate and geometry for magnonics and neuromorphic computing

   https://doi.org/10.1063/5.0274799  

   Sultana, Rawnak; Mondal, Amrit Kumar; Bhat, Vinayak Shantaram; Stenning, Kilian; Li, Yue; Arroo, Daan M; Vasdev, Aastha; McCarter, Margaret R; De_Long, Lance E; Hastings, J Todd; et al (August 2025, Journal of Applied Physics)

   Artificial spin ice, arrays of strongly interacting nanomagnets, are complex magnetic systems with many emergent properties, rich microstate spaces, intrinsic physical memory, high-frequency dynamics in the GHz range, and compatibility with a broad range of measurement approaches. This Tutorial article aims to provide the foundational knowledge needed to understand, design, develop, and improve the dynamic properties of artificial spin ice. Special emphasis is placed on introducing the theory of micromagnetics, which describes the complex dynamics within these systems, along with their design, fabrication methods, and standard measurement and control techniques. The article begins with a review of the historical background, introducing the underlying physical phenomena and interactions that govern artificial spin ice. We then explore the standard experimental techniques used to prepare the microstate space of the nanomagnetic array and to characterize magnetization dynamics, both in artificial spin ice and more broadly in ferromagnetic materials. Finally, we introduce the basics of neuromorphic computing applied to the case of artificial spin ice systems with a goal to help researchers new to the field grasp these exciting new developments. 

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5. Evidence for field induced quantum spin liquid behavior in a spin-1/2 honeycomb magnet

   https://doi.org/10.59717/j.xinn-mater.2024.100082  

   Lin, Gaoting; Shu, Mingfang; Zhao, Qirong; Li, Gang; Ma, Yinina; Jiao, Jinlong; Li, Yuting; Duan, Guijing; Huang, Qing; Sheng, Jieming; et al (January 2024, The Innovation Materials)

   One of the most important issues in modern condensed matter physics is the realization of fractionalized excitations, such as the Majorana excitations in the Kitaev quantum spin liquid. To this aim, the 3d-based Kitaev material Na₂Co₂TeO₆ is a promising candidate whose magnetic phase diagram of B // a* contains a field-induced intermediate magnetically disordered phase within 7.5 T < |B| < 10 T. The experimental observations, including the restoration of the crystalline point group symmetry in the angle-dependent torque and the coexisting magnon excitations and spinon-continuum in the inelastic neutron scattering spectrum, provide strong evidence that this disordered phase is a field induced quantum spin liquid with partially polarized spins. Our variational Monte Carlo simulation with the effective K-J₁-Γ-Γ'-J₃ model reproduces the experimental data and further supports this conclusion. 

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