John H. Van Vleck was a preeminent American theoretical physicist born on March 13, 1899, in Middletown, Connecticut, into an academic family with his father and grandfather serving as professors at Wesleyan University. He earned his PhD from Harvard University in 1922 under Edwin C. Kemble, completing his dissertation on the binding energy of a helium atom model suggested by both Kemble and Niels Bohr. Van Vleck began his academic career at the University of Minnesota in 1923, followed by positions at the University of Wisconsin from 1928 to 1934, before joining Harvard University where he spent the remainder of his distinguished career. At Harvard, he served as Professor of Physics (1934-1951), Chairman of the Physics Department (1945-1949), Dean of Engineering and Applied Physics (1951-1957), and ultimately as Hollis Professor of Mathematics and Natural Philosophy (1951-1969), cementing his legacy as one of America's most influential physicists of the twentieth century.
Van Vleck established the fundamental principles of the quantum mechanical theory of magnetism during the early 1930s, revolutionizing the scientific understanding of magnetic phenomena in solids. His seminal 1932 book, "The Theory of Electric and Magnetic Susceptibilities," provided the first comprehensive quantum mechanical treatment of magnetic properties and has remained a cornerstone reference in theoretical physics for decades. He developed the concept of temperature-independent susceptibility, now known as Van Vleck paramagnetism, and pioneered the crystal field theory that became essential for understanding the electronic structure of transition metal ions in solids. During World War II, his work at the MIT Radiation Laboratory revealed critical atmospheric absorption properties at specific radar wavelengths, with important consequences for both military radar systems and the emerging field of radio astronomy.
As a founding figure in modern magnetism research, Van Vleck's theoretical frameworks laid the groundwork for the entire field of solid-state physics, with applications spanning modern electronics and materials science. His contributions to understanding electron behavior in magnetic solids earned him the Nobel Prize in Physics in 1977, which he shared with Philip W. Anderson and Sir Nevill F. Mott, recognizing his fundamental work that transformed the theoretical understanding of magnetic and disordered systems. Van Vleck's legacy endures through numerous concepts bearing his name, including Van Vleck paramagnetism, Van Vleck transformations, and the Van Vleck formula, which continue to be essential tools for physicists worldwide. His receipt of the National Medal of Science in 1966 and the Lorentz Medal in 1974 further cemented his status as the most eminent American theoretical physicist between J. Willard Gibbs and the postwar generation, with his work continuing to influence contemporary research in quantum materials and condensed matter physics.
