Artificial spin ices (ASIs) are arrays of Ising-like magnetic nanoislands that are of interest for investigating fundamental physics as well as designing information processing devices. Recent efforts have pushed ASIs beyond the Ising model by using systems capable of possessing both Ising and complex spin textures (CSTs) such as vortices, which alters the nature of dipolar coupling and gives rise to exotic physics in existing ASI lattices [1-3]. CST-Ising studies in metal-based ASIs have primarily focused on field-dependent properties, as temperature-dependent experiments present challenges for metal-based systems. However, we have found that ASIs fabricated from the epitaxial complex oxide La0.7Sr0.3MnO3 (LSMO) can facilitate studies of CST-Ising formations in thermally active ASIs. CST-Ising formations in thermalized LSMO ASIs occurs through a careful balance of inter- and intra-island energetics enabled by the LSMO magnetic parameters [1]. Using x-ray photoemission electron microscopy (XPEEM) to perform magnetic domain imaging, we studied the thermal evolution of ex situ magnetized LSMO-based brickwork ASIs using a series of short (~5 min) annealing steps at 350 K (near LSMO bulk Tc ~ 370 K). We observed that the spin texture evolution can be tuned through the ASI lattice parameter, a. While ASIs with a = 600 nm formed only Ising states and experienced a few spin flips (~1 % of nanoislands) between annealing steps, ~20% of initially Ising nanoislands transformed into CSTs after the first annealing step for ASIs with a = 638 nm. Furthermore, we observed that thermal fluctuations in nanoisland domain states can occur through several different routes including Ising spin flips and transformations in magnetization topology (i.e., Ising-to-CST, CST-to-Ising, and CST-to-CST states). These results suggest the potential to introduce exotic kinetics in existing ASI lattices and would provide further insights into designing magnetically-reconfigurable computing architectures.

Imaging thermally induced Ising

The fundamental building blocks of artificial spin ice (ASI) systems are magnetic nanoislands designed for Ising-like single domain configurations magnetized along the nanoisland length due to shape anisotropy. The dipolar interaction between these macrospins serve as the basis for investigating geometric frustration in ASIs with a variety of array geometries ranging from square-like arrangements to quasicrystals. Using X-ray photoemission electron microscopy (X-PEEM) to perform magnetic domain imaging, we studied thermally demagnetized La0.7Sr0.3MnO3-based brickwork ASIs and showed that non-Ising domains, which we call complex spin textures (CSTs), can be stabilized through appropriate selection of nanoisland width, W, and ASI lattice parameter, a. While W-dependent formation of CSTs can be explained due to the dominance of shape anisotropy, the a-dependence was unexpected for nanoislands possessing identical W, suggesting that inter-island effects play an important role. MuMax3 micromagnetic simulations indicated that an intermediate range of 100 nm ≤ W &lt; 150 nm and 600 nm ≤ a ≤ 700 nm exists where the formation of Ising states are preferred over CSTs as shown in Fig. 1. For larger values of W and a that reside above the black border in the energy diagram of Fig. 1, CST formation becomes energetically favorable over an arrangement of Ising states in higher energy vertex configurations. Energy analysis suggests that while magnetostatic energy dominates the energetics, the small contribution from exchange energy determines whether nanoislands can exist in Ising or CST states. The nanoisland magnetic state changes the magnetostatics arising from both intra-island shape anisotropy and inter-island dipolar interaction. These results suggest the potential to create tunable nanoisland domain states, providing a new direction in the development of ASI systems with exotic phase transitions as well as novel nanomagnetic logic architectures.

![](https://assets.underline.io/uploads/markdown_image/1/image/12c68623b9c39a06d7d5874092f9e981.jpg)

Energetics of complex spin textures in LSMO artificial spin ice structures

Energetics of complex spin textures in LSMO artificial spin ice structures

Artificial spin ices (ASIs) are lithographically patterned arrays of single domain magnetic nanoislands where the dipolar interactions between these Ising-like macrospins have served as the basis for investigating phenomena such as geometric frustration and emergent magnetic monopoles [1]. While the majority of ASI studies have utilized nanoislands composed of soft magnetic metals (e.g. permalloy), the use of complex oxides, such as La0.7Sr0.3MnO3 (LSMO), could permit room temperature studies of thermally-active ASIs (TC ~ 360 K) and serve as a platform for coupling the rich physics of both complex oxide heterostructures and ASI structures. In this work, we utilize x-ray photoemission electron microscopy (X-PEEM) to image LSMO-based brickwork ASI structures where a breakdown of the Ising model of individual nanoislands occurs at a critical coupling strength which balances intra- and inter-island magnetic interactions. For ASI structures with nanoislands of identical dimensions, the ASI lattice parameter controls the inter-island coupling strength, resulting in systems composed solely of single-domain magnetic nanoislands, or a mixture of single-domain and complex spin textures (CST, i.e. single and double vortex states). Analysis of magnetic ordering in X-PEEM images reveals that nucleation of CST in frustrated nanoislands is accompanied by a disruption in long-range ordering. While it is generally assumed that inter-island interactions in ASI systems only influence the ordering of the nanomagnetic ensemble, in this LSMO-based ASI system inter-island coupling can dictate both the spin texture within individual nanoislands and long-range magnetic ordering. These results suggest the potential to create tunable nanoisland domain states, providing a new direction in developing ASI systems with exotic phase transitions as well as novel nanomagnetic logic architectures.References: 1. Skjærvø, S.H., et al., Nature Reviews Physics., Vol. 2, p.13 (2020)

The Formation of Complex Spin Textures in La0.7Sr0.3MnO3 Artificial Spin Ice Arrays

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Imaging thermally induced Ising

Energetics of complex spin textures in LSMO artificial spin ice structures

The Formation of Complex Spin Textures in La0.7Sr0.3MnO3 Artificial Spin Ice Arrays

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