Van Vleck, John Hasbrouck (1899–1980)

US physicist, considered one of the founders of modern magnetic theory (see magnetism). He was awarded the Nobel Prize for Physics in 1977 for his contributions to understanding the electronic structure of magnetic and disordered systems. He shared the award with his student Philip Anderson.

Van Vleck was born in Middletown, Connecticut, and studied at the University of Wisconsin and at Harvard. He became professor at Minnesota 1927 and was professor at Harvard 1934–69.

Using wave mechanics, Van Vleck devised a theory that gives an accurate explanation of the magnetic properties of individual atoms in a series of chemical elements. He also introduced the idea of temperature-independent susceptibility in paramagnetic materials – now called Van Vleck paramagnetism. His formulation of the ligand field theory is one of the most useful tools for interpreting the patterns of chemical bonds in complex compounds. This theory explains the magnetic, electrical, and optical properties of many elements and compounds by considering the influences exerted on the electrons in particular atoms by other atoms nearby.