Cornelis Jacobus (Cor) Gorter (14 August 1907, Utrecht – 30 March 1980, Leiden) was a Dutch experimental and theoretical physicist. Among other work, he discovered paramagnetic relaxation and was a pioneer in low temperature physics.
After his Abitur in The Hague, Gorter studied physics in Leiden, earning his PhD with the thesis Paramagnetische Eigenschaften von Salzen ("Paramagnetic Properties of Salts") under Wander de Haas. From 1931 to 1936 he worked at Teylers Stichting in Haarlem and from 1936 to 1940 at the University of Groningen, before he became a professor at the University of Amsterdam as successor to Pieter Zeeman. In 1946, succeeding W. H. Keesom, he returned to Leiden as a professor. In 1948, as successor to De Haas, Gorter directed the Kamerlingh Onnes Laboratory, remaining there until his retirement in 1973. He died in Leiden in 1980, after suffering for several years from Alzheimer's disease. His doctoral students include Nicolaas Bloembergen and Bert Broer.
In 1936 he discovered paramagnetic relaxation; however, he missed the discovery of nuclear magnetic resonance (otherwise known as nuclear spin resonance), as described by Joan Henri Van der Waals.
With Hendrik Casimir he devised a two-fluid model to explain superconductivity with thermodynamics and Maxwell's equations. Casimir described their collaboration in one of his books. The "Gorter-model" for a second-order phase transition is from this period of his career, as well as the elucidation of the Senftleben effect (change of viscosity and thermal conductivity of paramagnetic gas in a magnetic field).