A magnet that stacks up like a pile of pancakes: that's how the material CrSBr is structured. At low temperatures, each layer is magnetized, but neighboring layers point in opposite directions, and their magnetic fields cancel each other out. This order is called antiferromagnetic, and it's fragile: just a slight warming demagnetizes the layers. Scientists were looking for a way to strengthen this stack so it could hold its magnetization at higher temperatures.
The solution came from chemistry: they inserted charged organic molecules between the layers, like thin spacers between pancakes. These molecules, tetramethylammonium and tetrapropylammonium, push the layers apart and change their interaction. Instead of pointing in opposite directions, the layers aligned in the same direction — resulting in a ferromagnet. The temperature at which the material loses its magnetic properties rose from 140 to 190 and even 230 Kelvin (minus 83 and minus 43 degrees Celsius). For comparison, a typical room-temperature magnet works at 300 Kelvin, so the gap has narrowed.
The new material is stable in air and shows a strong change in electrical resistance in a magnetic field — more than 60% at 50 Kelvin. This means it could be used to make magnetic field sensors or memory elements that don't degrade on contact with air. For now, such devices require significant cooling, but this work points the way toward more practical temperatures.
A temperature of 230 Kelvin is minus 43 degrees Celsius — colder than the coldest winter in Antarctica. But for magnetic materials, it's a step toward warmth: previously, they only worked at minus 133 degrees.
Science fiction often features materials that change properties at a touch. Here, scientists literally inserted 'switch' molecules between the layers of a magnet, like a construction set where one piece changes the whole picture.