Imagine two impossibly thin sheets of material, each one a thousand times thinner than a human hair, stacked on top of each other. Now picture twisting one of them by just 3 degrees — about the width of a fingernail viewed from across a room. That tiny rotation changes everything, according to researchers at TU Darmstadt in Germany.
In a study published in Nature Communications, an international team discovered that this small twist creates a kind of memory effect in the material, called hysteresis. That means the material can hold onto information about which direction its magnetism was pointing, even after you stop applying a magnetic field. It's the same property that makes hard drives store your photos and documents — and finding it in such an ultra-thin material opens exciting new possibilities for future technology.
The material in question is chromium sulfide bromide, nicknamed CrSBr. Normally, when you stack two layers of this material, their magnetic fields point in opposite directions and cancel each other out — a behavior called antiferromagnetism. But when the researchers twisted one layer just slightly, something surprising happened. The twist created what scientists call a moiré pattern, a fine structural interference that altered how the two layers interacted magnetically.
"We observed hysteresis particularly clearly in the twisted structure," the team noted — a behavior they didn't see in untwisted layers.
The discovery connects basic science to real-world applications. Researchers Priyanka Mondal, Wenze Lan, and Lennard Hopf, working in Professor Bernhard Urbaszek's Hybrid Quantum Systems group, used light-based measurements at extremely cold temperatures to watch the material respond to magnetic fields. Their theoretical model accurately predicts how the material switches between magnetic states. Meanwhile, similar twist-engineering techniques have already produced other remarkable results, including materials where electricity flows with zero resistance (superconductivity) and materials that block current even though classical physics says they shouldn't (Mott insulators).
Looking ahead, the team envisions CrSBr and related materials forming the backbone of new memory devices, flexible electronic components, and something called spintronics — a new type of electronics that processes information using magnetic properties rather than electrical charges, potentially using far less energy than today's devices.