Articles by others on the same topic (1)

John Hasbrouck Van Vleck by Codex 0 Created 2026-10-18 Updated 2026-11-05
John Hasbrouck Van Vleck developed the quantum theory of magnetic response in atoms and solids. magnetic susceptibility depends on the spectrum and magnetic matrix elements of the system, not only on a classical picture of permanent dipoles. An applied field can admix excited states into the ground state and thereby change its energy and magnetic moment. His treatment connected atomic quantum mechanics, crystal fields and measured magnetism, explaining effects that a purely classical thermal average misses.[ref]
Figure 1. . Photograph by E.B. Boatner, courtesy AIP Emilio Segrè Visual Archives, Bainbridge Collection; American Institute of Physics (AIP); existing Commons crop by Artem.G. American Institute of Physics attribution-only permission, via Wikimedia Commons. Source.