Heisenberg pseudo-exchange and emergent anisotropies in field-driven pinwheel artificial spin ice

Abstract

Rotating all islands in square artificial spin ice (ASI) uniformly about their centres gives rise to the recently reported pinwheel ASI. At angles around 45${}^{\mathrm{o}}$, the antiferromagnetic ordering changes to ferromagnetic and the magnetic configurations of the system exhibit near-degeneracy, making it particularly sensitive to small perturbations. We investigate through micromagnetic modelling the influence of dipolar fields produced by physically extended islands in field-driven magnetisation processes in pinwheel arrays, and compare the results to hysteresis experiments performed in-situ using Lorentz transmission electron microscopy. We find that magnetisation end-states induce a Heisenberg pseudo-exchange interaction that governs both the inter-island coupling and the resultant array reversal process. Symmetry reduction gives rise to anisotropies and array-corner mediated avalanche reversals through a cascade of nearest-neighbour (NN) islands. The symmetries of the anisotropy axes are related to those of the geometrical array but are misaligned to the array axes as a result of the correlated interactions between neighbouring islands. The NN dipolar coupling is reduced by decreasing the island size and, using this property, we track the transition from the strongly coupled regime towards the pure point dipole one and observe modification of the ferromagnetic array reversal process. Our results shed light on important aspects of the interactions in pinwheel ASI, and demonstrate a mechanism by which their properties may be tuned for use in a range of fundamental research and spintronic applications.

arXiv comment14 pages, 13 figures; post revision

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Cited by in corpus (8)

• Dynamics of reconfigurable artificial spin ice: towards magnonic functional materials
• Fast Pixelated Detectors in Scanning Transmission Electron Microscopy. Part II: Post Acquisition Data Processing, Visualisation, and Structural Characterisation
• Ice-rule made manifold: phase transitions, topological defects and manifold restoration in two-dimensional artificial spin systems
• Spin-wave dynamics and symmetry breaking in an artificial spin ice
• Signatures of long range dipolar interactions in artificial square ice
• Artificial Spin Ice: A Tutorial on Design and Control of Geometry, Microstate, Magnon Dynamics & Neuromorphic Computing
• Field-driven Reversal Models in Artificial Spin Ice
• Coupling-dependent antiferromagnetic-ferromagnetic ordering in a pinwheel artificial spin ice