Abstract
Electricity and magnetism are common features of our world. The subject of electromagnetic fields in empty space populated only by point charges or smooth charge distributions in space is well understood. In that case, one deals with the classical theory of electrodynamics developed by J.C. Maxwell in 1864. Electromagnetism in the presence of matter is, however, a completely different problem. Microscopic electric behavior of homogeneous substances can in general be characterized fairly simply and completely. The theory that enables us to do this is fairly well understood. Sadly the situation is quite different for magnetism in matter. The study there is phenomenological. That is, the substance is characterized by a number of parameters and the experimentally determined relations among them. We are not aware of any successful microscopic theory of magnetism in matter. The microscopic theory of magnetic substances, a topic of fundamental and technological importance, is the subject of this paper.
Highlights
The history of magnetism dates back to the year 600 B.C
But by no means exhaustive, we consider a striking feature of ferromagnetism which distinguishes it from diamagnetism and paramagnetism: A given ferromagnetic substance, e.g. pure iron, loses its ferromagnetism abruptly at a certain critical temperature called its Curie point
Our first task is to explain why one does not observe magnetic effects in the neighbourhood of an infinite rod of unmagnetized ferromagnetic substance, e.g. iron, and why the magnetic field outside an unmagnetized rod of finite length looks the same as that of the electric field outside an electric dipole consisting of two point charges, +Q and −Q
Summary
The history of magnetism dates back to the year 600 B.C. In that year, Thales of Miletus, often called the father of Greek science, detected magnetism in lodestone (magnetite). We infer from this observation that the magnetic field has a source which is related to it the way electric charge is related to electric field This enabled Ampere to hypothesize that magnetism in matter is caused by a number of tiny rings of electric current distributed throughout the substance, implying that an ensemble of tiny rings of electric current is the source of magnetism. But by no means exhaustive, we consider a striking feature of ferromagnetism which distinguishes it from diamagnetism and paramagnetism: A given ferromagnetic substance, e.g. pure iron, loses its ferromagnetism abruptly at a certain critical temperature called its Curie point. This transition temperature is different for different substances. We give a complete and comprehensive quantum theory of magnetism in matter
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