Magnetic Materials: A Tale of Two Universality Classes

A material that can switch between two magnetic states, like flipping a switch. This happens when the material gets hotter, and scientists call this the Curie temperature. Understanding this switch is tricky because it happens on tiny scales that conventional tools can't easily see. In this study, scientists used a special tool called a scanning nitrogen-vacancy center to watch this switch in action. They found that the material's magnetic textures change in a way that follows something called a 3D universality class. This means that as the material gets hotter, the magnetic areas start to work together over larger distances. But when they looked at how the magnetic spins moved, they found something different – it followed an XY universality class. This is like saying that while the magnetic areas are working together, the spins are moving in a different pattern. These results help us understand the rules that govern how materials change from one state to another, which is important for making better materials in the future.