Physicists in the US and Taiwan have performed new experiments that verify long-standing theoretical predictions of how long-range magnetic order can emerge in atomically thin materials. Led by Edoardo Baldini at the University of Texas at Austin, the researchers showed how the transformation occurs through two distinct phase transitions – possibly paving the way for new generations of ultracompact magnetic materials. Atomically thin two-dimensional (2D) materials are widely studied for their diverse electrical, optical, mechanical and thermal properties. So far, however, their magnetic properties have generally remained far more elusive. Underlying the problem are inevitable thermal fluctuations, which make it extremely difficult to sustain magnetic order over distances larger than atomic scales. For decades, theorists have investigated a possible exception to this rule in “2D XY” systems: featuring flat arrays of spins that can rotate continuously within the plane and interact with neighbouring spins.…