Elementary Properties of Electromagnetic Continua

Abstract

This chapter is concerned with the physical nature of electromagnetic bodies. It is intended to provide some fundamental concepts relevant to the electromagnetic properties of matter. We begin with a discussion of dielectric materials in Section 4.2 and, using classical ideas of polarizability in Section 4.3, we obtain expressions of dielectric susceptibility and permittivity. The classical Clausius—Mossoti equation is given. The nature of ferroelectric crystals, their thermal behavior and electrostriction, piezoelectricity, and pyroelectricity are discussed on the basis of simple atomic models. In Section 4.4 we turn our attention to magnetism and briefly discuss the quantum mechanical origin of magnetism, gyromagnetic effects, and various types of magnetism (e.g., paramagnetic, antiferromagnetic, and ferrimagnetic materials). The nature of ferromagnetic materials, the Curie—Weiss law, the Heisenberg model of spin—spin interaction, and the thermal effects on the magnetic susceptibilities of various types of magnetic materials are discussed in Section 4.5. Magnons or spin waves, magnetostrictive effects, piezomagnetism, and magnon—phonon couplings are touched on briefly in the same section.