Department of Physice
The electrical and magnetic properties of different materials are determined by how the electrons move about in relation to the atomic nucleus. When an atom from a foreign substance is inserted into a crystalline structure, the crystal's properties can be altered. During the 1930s John van Vleck developed theories about how electrical fields in a crystal affect a foreign atom and how such an atom can be bound to nearby atoms through its electrons. He also showed how the interaction between the electron's movements can create local magnetic moments in crystals.