A sheet of paper with magnetic properties: that's roughly what the new material 1T-CrS₂ is like. Its layers are held together by weak forces, like the pages of a notebook, but each layer is a true magnet. And a hard magnet at that: it maintains magnetization perpendicular to the layers and doesn't lose it even when heated above room temperature.
Growing such crystals had long been elusive. Now a team of physicists has done it using chemical vapor deposition, without catalysts — a clean recipe. Measurements show that when cooled below 80 K, the material transitions from a semimetallic state to an insulating one. In a magnetic field, its resistance drops — an effect that persists up to 350 K.
The most intriguing part begins below 30 K: a topological Hall effect emerges. Electrons feel something like an extra magnetic field, born from the special twisting of spins (the particles' intrinsic magnetic moments) in the material. Calculations show that two mechanisms are responsible. Spin-orbit coupling opens an energy gap at the crossing points of electronic bands. Electronic correlations reshape the Fermi surface, removing extra pockets and enhancing spin polarization. Together, they create the conditions for topological transport.
Such a union of correlations and spin-orbit coupling in a layered magnet is rare. 1T-CrS₂ becomes a model system for studying how macroscopic effects arise from quantum properties. And that very "sheet of paper" turns out to be not just a magnet but a whole laboratory in your hand — with spin vortices and electronic surprises yet to be unraveled.
The topological Hall effect is like a car turning not because of a tilted road, but because of swirling currents in the asphalt itself.