Only elements with unpaired electrons exhibit paramagnetism, ferromagnetism, and antiferromagnetism. LSM has a rich electronic phase diagram, including a doping-dependent metal-insulator transition, paramagnetism and ferromagnetism. Thus, now the spins would be "parallel" (ferromagnetism in a solid, paramagnetism in two-atomic gases). Compounds which are expected to be diamagnetic may exhibit this kind of weak paramagnetism. Both dioxygen and the superoxide anion are free radicals that exhibit paramagnetism. The explanation of the paramagnetism of dioxygen was a major success for molecular orbital theory. Pauli paramagnetism is named after the physicist Wolfgang Pauli. In addition, the C term is observed only for molecules with ground state paramagnetism. Van Vleck transformations, Van Vleck paramagnetism and Van Vleck formula are named after him. Using this idea, he developed the theory of paramagnetism in 1926. The paramagnetism gives rise to very diverse chemical shifts. The paramagnetism is due to a net "orbital" (and not spin) electronic angular momentum. This effect is a weak form of paramagnetism known as "Pauli paramagnetism".