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Abstract
AbstractA set of topological arrangements of individual ferromagnetic islands in ideal and disordered artificial spin ice (ASI) arrays is investigated in order to evaluate how aspects of their field‐driven reversal are affected by the model used. The set contains the pinwheel and square ice tilings, and thus a range of magnetic ordering and reversal properties are tested. It is found that a simple point dipole model performs relatively well for square ice, but it does not replicate the properties observed in recent experiments with pinwheel ice. Parameterization of the reversal barrier in a Stoner–Wohlfarth model improves upon this, but fails to capture aspects of the physics of ferromagnetic coupling observed in pinwheel structures which have been attributed to the non‐Ising nature of the islands. In particular, spin canting is found to be important in pinwheel arrays, but not in square ones, due to their different symmetries. The authors' findings will improve the modeling of ASI structures for fundamental research and in applications which are reliant upon the ability to obtain and switch through known states using an externally applied field.
Highlights
A set of topological arrangements of individual ferromagnetic islands in ideal of the system through application of heat or an external field
The second reversal criterion we consider is a parametrization of the reversal barrier astroids[46] in a Stoner– Wohlfarth (SW) model of coherent rotation within an extended volume,[47] following that recently implemented in the Python package flatspin;[41] we will refer to this as the Stoner–Wohlfarth point-dipole (SW-point dipole (PD)) model
Including a Stoner–Wohlfarth barrier when using point dipoles is important for square arrays with disorder, and is critical to approximating the inter-island coupling in pinwheel arrays
Summary
We define the different models and ASI tilings used throughout this work. We will refer to the first of these models as the point dipole (PD) model, and adopt the reversal criterion of the net field along the long-axis of the island exceeding a threshold, as commonly used in field-driven square and kagome arrays.[13,45] The second reversal criterion we consider is a parametrization of the reversal barrier astroids[46] in a Stoner– Wohlfarth (SW) model of coherent rotation within an extended volume,[47] following that recently implemented in the Python package flatspin;[41] we will refer to this as the Stoner–Wohlfarth point-dipole (SW-PD) model In this model, it is important to note that the spins themselves are fixed and not allowed to rotate (other than an instantaneous 180o reversal). We will consider the inter-island coupling and any emergent anisotropies, the influence of spin canting, the reversal paths for ideal arrays, and how the results predicted by each model are affected by disorder
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