Twisted Materials: Large-Scale Magnetism Beyond the Moiré Pattern

A subtle twist in the arrangement of atomically thin magnetic crystals can generate magnetic patterns far larger and more complex than previously anticipated, opening novel avenues for low-power spintronic devices. Researchers at the University of Edinburgh, reporting in Nature Nanotechnology, have demonstrated that twisting these 2D materials doesn’t just reshape their electronic properties – it fundamentally alters their magnetism, creating what they’ve termed “super-moiré spin order.” This discovery challenges existing assumptions about how magnetism behaves in these engineered materials and suggests a new level of control over magnetic textures.

Moiré Engineering and the Emergence of Topological Magnetism

The foundation of this work lies in a technique called moiré engineering. When two atomically thin crystals are stacked with a slight rotational mismatch, an interference pattern emerges – the moiré pattern. Scientists have already leveraged this pattern to tune the electronic properties of these materials, creating novel quantum states. Now, magnetism responds to this twisting in equally surprising ways. The team focused on twisted bilayers of chromium triiodide (CrI₃), an antiferromagnetic material.

Antiferromagnetic materials are unique because their internal magnetic moments align in opposing directions, resulting in zero net magnetization. This characteristic, combined with the topological properties of the newly formed magnetic textures, is key to the potential for low-energy spintronic applications. Spintronics, or spin electronics, aims to utilize the intrinsic spin of electrons, rather than just their charge, to store and process information. Skyrmions, in particular, are nanoscale magnetic whirls that are topologically protected – meaning they are stable and resistant to disruption – and can be moved with very little energy.

Beyond the Expected Scale: Giant Skyrmions

Traditionally, the size of physical effects in moiré systems is expected to be dictated by the dimensions of the moiré unit cell – the repeating pattern created by the lattice overlap. However, the Edinburgh team’s experiments revealed something different. Using a technique called scanning nitrogen-vacancy magnetometry, which allows for nanoscale imaging of magnetic fields, they observed magnetic textures – specifically, skyrmion-like patterns – extending up to ~300 nanometers. This represents significantly larger than a single moiré cell and roughly ten times the underlying wavelength of the pattern.

This finding suggests that magnetism isn’t simply mirroring the moiré template. Instead, it’s governed by a more complex interplay of forces. The researchers identified key factors at play: exchange interactions (how neighboring electron spins interact), magnetic anisotropy (the tendency of a material to align its magnetization in a specific direction), and Dzyaloshinskii-Moriya interactions (a specific type of interaction that favors swirling magnetic textures). The twist angle subtly adjusts the balance of these forces, leading to the formation of these extended magnetic structures.

A Counterintuitive Angle Dependence

Perhaps the most surprising aspect of the research is the relationship between the twist angle and the size of the magnetic textures. As the twist angle decreases, the moiré wavelength increases – as expected. However, the size of the magnetic patterns doesn’t follow suit. Instead, it peaks around 1.1° and then disappears entirely above approximately 2°. This reversal indicates that the magnetism is actively responding to the twist, rather than passively following the moiré pattern.

To validate their experimental observations, the researchers performed large-scale spin dynamics simulations. These simulations confirmed the formation of extended Néel-type antiferromagnetic skyrmions, spanning multiple moiré cells, and supported the interpretation that the observed behavior arises from the delicate balance of competing magnetic interactions.

Implications for Low-Power Spintronics

The potential implications of this discovery are significant, particularly in the field of spintronics. Skyrmions are attractive candidates for future information storage and processing technologies due to their small size, stability, and low energy requirements for manipulation. The ability to create these skyrmions simply by adjusting the twist angle – without the need for lithography, heavy metals, or strong electric currents – offers a potentially cleaner and more energy-efficient approach to device fabrication.

Dr. Elton Santos, Reader in Theoretical/Computational Condensed Matter Physics at the University of Edinburgh, explained, “This discovery shows that twisting is not just an electronic knob, but a magnetic one. We’re seeing collective spin order self-organize on scales far larger than the moiré lattice. It opens the door to designing topological magnetic states simply by controlling angle, which is a remarkably simple handle with profound practical consequences.”

Super-Moiré Spin Order and the Future of 2D Magnetism

The researchers describe the observed phenomenon as “super-moiré spin order,” emphasizing that twist engineering operates across multiple length scales. A change in atomic alignment can generate topological structures on much larger, mesoscale distances. This challenges the conventional understanding of moiré physics as a purely local effect and positions twist angle as a powerful thermodynamic control parameter for tuning magnetic properties.

The larger size and topological protection of these Néel-type skyrmionic textures craft them particularly well-suited for integration into devices. Their increased size simplifies detection and manipulation, while their inherent stability and the insulating nature of the host material promise extremely low energy loss during operation.

Next Steps: From Lab to Device

The immediate next steps involve further characterizing the properties of these twisted magnetic systems and exploring the limits of twist-angle control. Researchers will likely focus on optimizing the twist angle to maximize skyrmion size and stability, as well as investigating different material combinations to enhance performance. Ongoing theoretical work will be crucial for refining our understanding of the underlying physics and guiding the design of new materials. The goal is to translate these fundamental discoveries into functional spintronic devices, paving the way for energy-efficient, post-CMOS computing technologies.