Sliding Bilayer Graphene Between Crystal Alignments Triggers Switchable Magnetic States

By shifting four sheets of carbon by a distance smaller than the width of a single atom—a movement roughly one-millionth the thickness of a human hair—physicists at Cornell University have transformed ordinary graphite into a permanent magnet. The technique uses a simple electrical pulse to slide the microscopic layers sideways.[1][4]

The microscopic movement toggles the material between a non-magnetic state and a ferromagnetic one. Because the carbon sheets stay locked in their new position after the current stops, the device acts as a non-volatile memory switch. It creates magnetism purely from geometry, without relying on traditional magnetic metals like iron or cobalt.[1][3]

"One of the things that makes this sliding technique interesting is that it is nonvolatile, meaning that the act of sliding and physically moving atoms creates a reliable memory source," said Daniel Brandon, a doctoral student at Cornell and the study's lead author. The discovery opens a new pathway for designing reconfigurable quantum materials.[1][4]

How sliding creates a magnet

The experiment relies on tetralayer graphene, a stack of exactly four atom-thick carbon sheets. Within each individual sheet, carbon atoms are bound by incredibly strong covalent bonds. However, the vertical stack is held together by much weaker van der Waals forces, allowing the layers to slip past one another under the right conditions.[1][3]

In its natural resting state, known as Bernal stacking, the alternating layers align in a pattern that leaves the material electronically ordinary and non-magnetic. Applying a gate voltage to the stack exerts an electrostatic force that physically shoves the layers into a new registry. This shifts the material into a rhombohedral stacking arrangement.[1][3]

"We discovered that if we focus on the much weaker bonds between the layers, known as van der Waals bonds, we were able to reconfigure the crystal structure," said Kenji Yasuda, an assistant professor of applied and engineering physics at Cornell. "Using voltage, we were able to shift alignment of the layers, something called 'sliding,' which changed how the graphene layers were stacked."[1][4]

That geometric shift completely rewrites the material's electronic landscape. In the rhombohedral configuration, the correlated behavior of the electrons generates an emergent ferromagnetic phase. The carbon itself does not change, but the new spatial arrangement forces its electrons to align their spins, producing a magnetic field from an elementally pure carbon system.[1][3]

Crucially, the researchers found that they could repeatedly write and erase this magnetic phase. By cycling the gate voltages through a specific sequence, the team toggled the device back and forth between the Bernal and rhombohedral states. The structural phase transition proved entirely reversible without causing permanent damage to the carbon lattice.[1][3][5]

Erasing the need for magnetic metals

Traditional magnetic memory, like the hard drives in older computers, relies on ferromagnetic elements such as iron, nickel, or rare-earth metals. Even newer two-dimensional magnets, such as chromium triiodide, require magnetic atoms to function. The Cornell device achieves magnetic switching with zero magnetic impurities, decoupling the property from specific chemical elements.[3]

Instead, the magnetism is an emergent consequence of the electrons interacting within the rhombohedral geometry. When the voltage pushes the layers back into the Bernal arrangement, those specific electron correlations break down, and the magnetism vanishes. The state of the device is determined entirely by its sweep history, acting as a structural toggle.[1][3]

The researchers confirmed the magnetic state through low-temperature electric transport measurements. They observed an anomalous Hall effect—a voltage that appears perpendicular to the current in the presence of magnetization—whose sign flipped under opposite displacement fields. This confirmed that the rhombohedral phase was genuinely ferromagnetic.[1]

Because the structural shift is non-volatile, the graphene remains magnetic even after the gate voltage is turned off. That persistence is the defining requirement for computer memory, where data must survive when a device loses power. The sliding mechanism effectively converts a structural degree of freedom into a stable magnetic data bit.[1][3][5]

Scaling up from cryogenic temperatures

While the structural sliding itself endures up to room temperature, the resulting magnetic phase currently requires extreme cold. The ferromagnetic properties in the tetralayer graphene only survive at a few kelvin, near absolute zero (-273 degrees Celsius). This limits the immediate application of the specific device in consumer electronics, which must operate in everyday environments.[3]

The coercive fields—the magnetic intensity required to flip the magnetization—also fluctuated from cycle to cycle during the experiments. The researchers attribute this variability to the small magnetic energy scale of the ferromagnetism in their sample. They noted that the domain configurations underlying the switching varied slightly between preparations.[1][3]

Despite these thermal limits, the underlying mechanism provides a vivid proof of concept. The strategy of using gate-induced sliding to drive a first-order transition between competing stacking arrangements can theoretically be applied to other van der Waals materials. Physicists can now look for different layered compounds where stacking governs exotic phases at higher temperatures.[3]

The fabrication of these devices requires extreme precision, as the four carbon sheets must be aligned with near-perfect twist angles. The Cornell team performed part of the work at the Cornell NanoScale Facility, supported by the National Science Foundation, carefully stacking the graphene layers to ensure the van der Waals bonds could slide smoothly.[1][4]

As research into rhombohedral graphene accelerates, the ability to switch between stacking regimes without physically rebuilding the device offers a new dimension of control. The U.S. Department of Energy primarily funded the October 2026 study, signaling broad institutional interest in how these reconfigurable quantum materials might eventually reshape computing architecture.[1][3][4]