When scientists shrink materials down to extremely thin layers—sometimes just a single atom thick—their behavior can become very unusual.
A new study has now revealed a strange form of magnetism in such an ultrathin material, confirming a theory that physicists first proposed more than 50 years ago.
The discovery was made by a research team led by scientists at University of Texas at Austin and published in the journal Nature Materials.
The researchers observed a sequence of exotic magnetic states in a material called Nickel Phosphorus Trisulfide (NiPS3) when it was cooled to extremely low temperatures.
NiPS3 belongs to a class of materials that can be peeled into layers only one atom thick. At this tiny scale, the magnetic behavior of the material changes dramatically, allowing scientists to observe new physical effects that cannot be seen in thicker materials.
In the experiment, the researchers cooled a thin sheet of NiPS3 to temperatures between about –150°C and –130°C. As the material cooled, it entered a special magnetic state known as the Berezinskii–Kosterlitz–Thouless phase, often called the BKT phase.
In this unusual state, the tiny magnetic directions of atoms—known as magnetic moments—do not simply align like the poles of a bar magnet.
Instead, they form swirling patterns called vortices. Each vortex spins in either a clockwise or counterclockwise direction, and they tend to appear in pairs that remain closely bound together.
The BKT phase was predicted decades ago by physicists Vadim Berezinskii, J. Michael Kosterlitz, and David Thouless. Kosterlitz and Thouless later received the Nobel Prize in Physics in 2016 for their work describing this unusual type of phase transition.
According to the research team, the magnetic vortices that appear in this phase are extremely stable and incredibly small.
They are only a few nanometers wide while existing within a layer that is just one atom thick. Because of their tiny size and stability, these structures could someday be used to control magnetism at the nanoscale.
When the scientists cooled the material even further, they observed a second magnetic state known as a six-state clock ordered phase. In this phase, the magnetic moments of atoms can point in only six specific directions, similar to the positions on a clock face.
Seeing both of these magnetic states in sequence is significant because it confirms a theoretical idea called the two-dimensional six-state clock model.
This model was first proposed by physicists in the 1970s as a way to understand magnetism in two-dimensional systems. Until now, scientists had observed parts of the predicted behavior, but not the complete sequence of phases.
The new experiment shows that the theory works in real materials.
Researchers believe the discovery could open the door to new types of ultracompact technologies.
If scientists can eventually stabilize these magnetic phases at higher temperatures—perhaps even room temperature—it could lead to innovative nanoscale devices for information storage or quantum technologies.
The study also suggests that many other atomically thin magnetic materials may host similar hidden phases, giving physicists new opportunities to explore the strange and fascinating behavior of matter in two dimensions.
