Selected papers by the COMET research group

Clocked dynamics in artificial spin ice

Johannes H. Jensen, Anders Strømberg, Ida Breivik, Arthur Penty, Miguel Angel Niño, Muhammad Waqas Khaliq, Michael Foerster, Gunnar Tufte & Erik Folven

Nature Communications 2024

Abstract: Artificial spin ice (ASI) are nanomagnetic metamaterials with a wide range of emergent properties. Through local interactions, the magnetization of the nanomagnets self-organize into extended magnetic domains. However, controlling when, where and how domains change has proven difficult, yet is crucial for technological applications. Here, we introduce astroid clocking, which offers significant control of ASI dynamics in both time and space. Astroid clocking unlocks a discrete, step-wise and gradual dynamical process within the metamaterial. Notably, our method employs global fields to selectively manipulate local features within the ASI. Sequences of these clock fields drive domain dynamics. We demonstrate, experimentally and in simulations, how astroid clocking of pinwheel ASI enables ferromagnetic domains to be gradually grown or reversed at will. Richer dynamics arise when the clock protocol allows both growth and reversal to occur simultaneously. With astroid clocking, complex spatio-temporal behaviors of magnetic metamaterials become easily controllable with high fidelity.

Evolving Artificial Spin Ice for Robust Computation

Arthur Penty and Gunnar Tufte

International Journal of Unconventional Computing, 2023

Abstract: Artificial spin ice is a magnetic metamaterial showing particular promise as a novel substrate for unconventional computing. While simulations are invaluable for investigating new computational substrates, results must be robust to the noise and disorder of the physical world for device realization. Here, we investigate the computational robustness of artificial spin ice towards fabrication disorder. Using an evolutionary search, we explore different geometries of artificial spin ice for robust computation. We show that by neglecting to consider disorder in the search, we obtain geometries that suffer greatly when disorder is introduced. We then demonstrate that by explicitly including disorder as part of the evolutionary search process, we are able to discover novel geometries that are robust against disorder. We also find that these geometries perform well on new instances of disorder, and when they fail, we see signs of graceful degradation.

flatspin: A Large-Scale Artificial Spin Ice Simulator

Open Access: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.064408

Abstract: We present flatspin, a novel simulator for systems of interacting mesoscopic spins on a lattice, also known as artificial spin ice (ASI). A generalization of the Stoner-Wohlfarth model is introduced, and combined with a well-defined switching protocol to capture realistic ASI dynamics using a point-dipole approximation. Temperature is modelled as an effective thermal field, based on the Arrhenius-Néel equation. Through GPU acceleration, flatspin can simulate the dynamics of millions of magnets within practical time frames, enabling exploration of large-scale emergent phenomena at unprecedented speeds. We demonstrate flatspin's versatility through the reproduction of a diverse set of established experimental results from literature. In particular, the field-driven magnetization reversal of “pinwheel” ASI is reproduced, for the first time, in a dipole model. Finally, we use flatspin to explore aspects of “square” ASI by introducing dilution defects and measuring the effect on the vertex population.

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