Van Vleck paramagnetism

Van Vleck paramagnetism is a type of magnetic behavior in materials where the electrons' small, temporary magnetic responses are caused by quantum effects, specifically the mixing of different energy states. Unlike typical paramagnetism, which requires unpaired electrons, Van Vleck paramagnetism can occur in materials with paired electrons due to their ability to temporarily shift between energy levels when a magnetic field is applied. This results in a weak, positive magnetic response even in substances that seem non-magnetic initially, highlighting the subtle quantum interactions involved in their magnetic properties.