  In this article an overview of the historical development of the key ideas in
the field of magnetism is presented. The presentation is semi-technical in
nature.Starting by noting down important contribution of Greeks, William
Gilbert, Coulomb, Poisson, Oersted, Ampere, Faraday, Maxwell, and Pierre Curie,
we review early 20th century investigations by Paul Langevin and Pierre Weiss.
The Langevin theory of paramagnetism and the Weiss theory of ferromagnetism
were partly successful and real understanding of magnetism came with the advent
of quantum mechanics. Van Vleck was the pioneer in applying quantum mechanics
to the problem of magnetism and we discuss his main contributions: (1) his
detailed quantum statistical mechanical study of magnetism of real gases; (2)
his pointing out the importance of the crystal fields or ligand fields in the
magnetic behavior of iron group salts (the ligand field theory); and (3) his
many contributions to the elucidation of exchange interactions in d electron
metals. Next, the pioneering contributions (but lesser known) of Dorfman are
discussed. Then, in chronological order, the key contributions of Pauli,
Heisenberg, and Landau are presented. Finally, we discuss a modern topic of
quantum spin liquids.
