Exploring CrS 2 : A Magnetic Material with Weyl Fermions

Scientists have been excitedly studying topological states in two-dimensional systems that have magnetic properties. Why? Because they hold great potential for spintronics and nanotechnology. One of these materials is a two-dimensional ferromagnet called CrS 2 . It has something unique: multiple Weyl points (WPs). These are special spots where electrons behave in a peculiar way. Imagine identifying these Weyl points. That's what scientists did using first-principles calculations. They found three distinct points: W 1 , W 2 , and W 3 . These points are of different types: type-I, type-II, and type-III. You can see them clearly when you look at the edges of the material. CrS 2 has another interesting feature: it magnetizes easily in one direction, along the c-axis. When you rotate the magnetization in the x - y plane, something interesting happens. The W 1 and W 3 points open up gaps, and these gaps stay the same no matter which direction the magnetization goes. But the W 2 point can still cross at specific in-plane directions, which means the material keeps its Weyl state. Scientists also looked at how strain affects the material. They found that biaxial strain (stretching in two directions) doesn't bother the Weyl points much, as long as it's less than ±5%. But uniaxial strain (stretching in one direction) makes them disappear. In short, CrS 2 is a two-dimensional ferromagnetic material with multiple Weyl fermions. You can change the topological states with an external magnetic field. Isn't that cool?