Chapter

Introduction to Magnetism and Magnetic Materials

Kannan M. Krishnan

in Fundamentals and Applications of Magnetic Materials

Published in print August 2016 | ISBN: 9780199570447
Published online December 2016 | e-ISBN: 9780191813504 | DOI: https://dx.doi.org/10.1093/acprof:oso/9780199570447.003.0001
Introduction to Magnetism and Magnetic Materials

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We introduce the family of magnetic materials—diamagnets, paramagnets, ferromagnets, anti-ferromagnets, and ferrimagnets—and their response to magnetic fields. Beginning with a brief description of magnetic fields (H) and how they are generated in a controlled and well-defined manner, we describe the response of the material to the magnetic field, called magnetic induction, B, including the contribution of the substance (be it a gas, solid, or liquid). We develop two different formulations, starting either with current-carrying wires and the forces between them (SI) or with interactions between magnetic “poles” (CGS). In this process, we describe the magnetic dipole moment, m, the elementary magnetic quantity of interest in materials, and its volume average or magnetization, M, and establish the inter-relationship between these fundamental magnetic parameters: B = μ0(H + M) in SI, and B = H + 4πM, in the CGS system of units. Following these definitions and presentation of related conceptual ideas, we provide a general overview of the variety of magnetic behavior observed in different materials. We then introduce magnetic hysteresis, structure-sensitive properties defined by various points on the hysteresis curve, and a description of the role of demagnetization and the associated magnetostatic energy for objects of simple, well-defined shape, such as ellipsoids of revolution. Finally, we present an overview of the practical consequences of demagnetization and conclude by presenting Maxwell’s equations, in differential form, accompanied by a brief discussion.

Keywords: magnetic fields; magnetostatics; hysteresis; demagnetization; magnetic materials

Chapter.  17468 words.  Illustrated.

Subjects: Condensed Matter Physics

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