University of Stuttgart Discovers Super-Moiré Magnetic State in Twisted 2D Materials

Researchers at the University of Stuttgart have uncovered a previously unknown magnetic phenomenon in atomically thin materials that could redefine future data storage architectures. Published in Nature Nanotechnology, their work reveals how twisted double-bilayer chromium triiodide (CrI₃) generates magnetic textures spanning hundreds of nanometers – far exceeding the boundaries of the material's intrinsic moiré pattern.

Experimental Breakthrough

Using scanning nitrogen-vacancy magnetometry at cryogenic temperatures (~4K), the team mapped magnetic domains in CrI₃ bilayers with twist angles between 1.1° and 2°. At precisely 1.1° misalignment, they observed:

• 300nm magnetic textures – 5× larger than the underlying 60nm moiré unit cells
• Dot-like spin structures organized across multiple lattice periods
• Complete disappearance of ordered states beyond 2° twist angles

This emergent behavior contradicts prior moiré-confined magnetism models. Instead, researchers identified a "super-moiré" state where magnetic ordering decouples from atomic geometry due to competing quantum interactions.

Physics of the Super-Moiré State

Three key forces drive this phenomenon:

1. Exchange interactions: Govern spin alignment between neighboring atoms
2. Magnetic anisotropy: Fixes spin orientation along crystal axes
3. Dzyaloshinskii-Moriya interaction (DMI): Spin-orbit coupling effect inducing chiral spin textures

As twist angles decrease below 2°, DMI strength increases dramatically. When the moiré period shrinks sufficiently, DMI overpowers local exchange energies, forcing spins to reorganize across 4-5 moiré cells. This creates antiferromagnetic skyrmion-like structures – topological spin configurations prized for motion control in spintronics.

Storage Density Implications

The observed textures could enable data bits at ∼60nm pitch. Current HDD technologies max out around 100Gb/in², while this approach theoretically supports >1Tb/in² densities. Professor Jörg Wrachtrup notes: "As data volumes grow, future magnetic storage must achieve higher densities without reliability loss. These results directly address that challenge."

Manufacturing Considerations

While promising, hurdles remain:

• Operation currently requires cryogenic temperatures
• CrI₃ degrades in ambient air
• Precision twist control below 1° presents fabrication challenges

The team confirms the mechanism should apply to other van der Waals magnets like Cr₂Ge₂Te₆ or Fe₃GeTe₂, which offer higher Curie temperatures (-30°C to 60°C). Material substitutions could yield room-temperature operation – essential for commercial viability.

This breakthrough demonstrates twist angle as a tunable parameter for engineering magnetic states, potentially enabling next-generation storage devices that leverage quantum phenomena for unprecedented data density.