Kevin Anthony Hofhuis

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Hofhuis

First Name

Kevin Anthony

ORCID

0000-0002-1642-4786

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Publications 1 - 6 of 6

Direct observation of a dynamical glass transition in a nanomagnetic artificial Hopfield network
Saccone, Michael; Caravelli, Francesco; Hofhuis, Kevin Anthony; et al. (2022)
Nature Physics
Spin glasses, generally defined as disordered systems with randomized competing interactions(1,2), are a widely investigated complex system. Theoretical models describing spin glasses are broadly used in other complex systems, such as those describing brain function(3,4), error-correcting codes(5) or stock-market dynamics(6). This wide interest in spin glasses provides strong motivation to generate an artificial spin glass within the framework of artificial spin ice systems(7-9). Here we present the experimental realization of an artificial spin glass consisting of dipolar coupled single-domain Ising-type nanomagnets arranged onto an interaction network that replicates the aspects of a Hopfield neural network(10). Using cryogenic X-ray photoemission electron microscopy (XPEEM), we performed temperature-dependent imaging of thermally driven moment fluctuations within these networks and observed characteristic features of a two-dimensional Ising spin glass. Specifically, the temperature dependence of the spin glass correlation function follows a power-law trend predicted from theoretical models on two-dimensional spin glasses(11). Furthermore, we observe clear signatures of the hard-to-observe rugged spin glass free energy(1) in the form of sub-aging, out-of-equilibrium autocorrelations(12) and a transition from stable to unstable dynamics(1,13).
Geometrical control of disorder-induced magnetic domains in planar synthetic antiferromagnets
Hofhuis, Kevin Anthony; Wang, Xueqiao; Hrabec, Aleš; et al. (2022)
Physical Review Materials
Magnetic domains play a fundamental role in magnetization processes. However, unlike in ferromagnets (FMs), the formation of domains in antiferromagnets (AFMs) is poorly understood because they are not favored by magnetostatics and are difficult to detect experimentally. In this paper, we create a synthetic planar AFM with tunable lateral coupling between neighboring FM regions to establish the role played by magnetic disorder in the formation of AFM domains. By directly imaging the synthetic AFM in real space, we observe that the AFM lattice spontaneously breaks up into domains following ac demagnetization. These AFM domains nucleate and pin at locally disordered sites that define their size and shape, which is explained with the help of a Gaussian random field Ising model. Furthermore, we can manipulate the AFM domain morphology by varying the interaction strength, which can be tuned with the geometrical parameters of the synthetic AFM.
Intrinsic chiral field as vector potential of the magnetic current in the zig-zag lattice of magnetic dipoles
Mellado, Paula; Concha, Andrés; Hofhuis, Kevin Anthony; et al. (2023)
Scientific Reports
Chiral magnetic insulators manifest novel phases of matter where the sense of rotation of the magnetization is associated with exotic transport phenomena. Effective control of such phases and their dynamical evolution points to the search and study of chiral fields like the Dzyaloshinskii–Moriya interaction. Here we combine experiments, numerics, and theory to study a zig-zag dipolar lattice as a model of an interface between magnetic in-plane layers with a perpendicular magnetization. The zig-zag lattice comprises two parallel sublattices of dipoles with perpendicular easy plane of rotation. The dipolar energy of the system is exactly separable into a sum of symmetric and antisymmetric long-range exchange interactions between dipoles, where the antisymmetric coupling generates a nonlocal Dzyaloshinskii–Moriya field which stabilizes winding textures with the form of chiral solitons. The Dzyaloshinskii–Moriya interaction acts as a vector potential or gauge field of the magnetic current and gives rise to emergent magnetic and electric fields that allow the manifestation of the magnetoelectric effect in the system.
Plasmon‐Enhanced Optical Control of Magnetism at the Nanoscale via the Inverse Faraday Effect
Parchenko, Sergii; Hofhuis, Kevin Anthony; Larsson, Agne Åberg; et al. (2025)
Advanced Photonics Research
The relationship between magnetization and light has been the subject of intensive research for the past century. Herein, the impact of magnetization on light polarization is well understood. Conversely, the manipulation of magnetism with polarized light is being investigated to achieve all-optical control of magnetism, driven by potential technological implementation in spintronics. Remarkable discoveries, such as the single-pulse all-optical switching of magnetization in thin films and submicrometer structures, have been reported. However, the demonstration of local optical control of magnetism at the nanoscale has remained elusive. Herein, it is demonstrated that exciting gold nanodiscs with circularly polarized femtosecond laser pulses lead to ultrafast, local, and deterministic control of magnetization in an adjacent magnetic film. This control is achieved by exploiting the magnetic moment generated in plasmonic nanodiscs through the inverse Faraday effect. The results pave the way for light-driven control in nanoscale spintronic devices and provide important insights into the generation of magnetic fields in plasmonic nanostructures.
Real-space imaging of phase transitions in bridged artificial kagome spin ice
Hofhuis, Kevin Anthony; Skjærvø, Sandra Helen; Parchenko, Sergii; et al. (2022)
Nature Physics
In frustrated spin systems, magnetic phase transitions underpin the formation of exotic, frustration-driven magnetic phases. Of great importance is the ability to manipulate these transitions to access specific phases, which in turn provides a means to discover and control novel phenomena. Artificial spin systems incorporating lithographically fabricated arrays of dipolar-coupled nanomagnets that enable real-space observation of the magnetic configurations provide such an opportunity. In particular, the kagome spin ice is predicted to exhibit two phase transitions, one of which is to a low-temperature phase whose long-range ground-state order has not been observed experimentally. To achieve this ordered state, we change the global symmetry of the artificial kagome system by selectively tuning the near-field nanomagnet interactions through nanoscale bridges at the lattice vertices. By precisely tuning the interactions, we are able to quantify the influence of frustration on the phase transition, finding that the driving force for spin and charge ordering depends on the degeneracy strength at the vertex.
Tuning interactions in magnetic metamaterials
Hofhuis, Kevin Anthony (2021)

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Kevin Anthony Hofhuis

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