Uranium diselenide is a compound of uranium and selenium. It has a β form that has orthorhombic crystal system. The family of crystals it matches is PbCl2. The dimensions of the unit cell are a: 7.455 Å, b: 4.2320 Å, c= 8.964 Å. The compound has the unusual property of ferromagnetism, but only if the temperature is below 14 K.[1]
Tellurium can be substituted for selenium in varying quantities, expanding the lattice and increasing the ferromagnetic Curie temperature.[1]