Sabyasachi Chatterjee obtained his PhD in condensed matter physics from the Indian Institute of Science, Bangalore. He now works at the Indian Institute of Astrophysics. His current interests are in the areas of galactic physics and optics. He is also active in the teaching and popularising of science.

Heisenberg's contributions to the understanding of ferromagnetism are reviewed. The special features of ferromagnetism, vis-a-vis dia and para magnetism, are introduced and the necessity of a Weiss molecular field is explained. It is shown how Heisenberg identified the quantum mechanical exchange interaction, which first appeared in the context of chemical bonding, to be the essential agency, contributing to the co-operative ordering process in ferromagnetism.

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Address for Correspondence
S Chatterjee
Indian Institute of
Astrophysics
Bangalore 560 034
Email: chat@bgl.vsnl.net.in