# Comparison of Dielectric and Magnetic Properties

| Here is a quick and simple comparison of dielectric and magnetic definitions and laws
Dielectric Behavior | Magnetic Behavior
Charge q |  |  | No equivalent
Electrical field E |  |  | Magnetic field H
Electrical displacement D |  |  | (Magnetic) Induction B
Permittivity constant of vacuum e0 |  |  | Permeability constant of vacuum m0
Relative dielectric constant of material er |  |  | Relative permeability constant of material mr
From Maxwell equations |  |  | From Maxwell equations
Connection between dielectric flux density D, electrical field E, and relative dielectric constant er | D = e0 · er · E | B = m0 · mr · H | Connection between magnetic flux density B, magnetic field H, and relative (magnetic) permeability mr
Formulation with electrical Polarization P in the material caused by the electrical field | D = e0 · E + P | B = m0 · H + J | Formulation with magnetic polarization J in the material caused by the magnetic field
Justified by theory of polarization mechanisms | Justified by theory of magnetization mechanisms
Material "law" describing P as response of a material to a field E and defining the dielectric susceptibility c Note exception: Ferroelectricity | P = e0 ·c · E | J = m0 · cmag · H | Material "law" describing J as response of a material to a field H and defining the magnetic susceptibility cmag Note exception: Ferromagnetism
Relation between c and er | c = er – 1 | cmag = mr – 1 | Relation between cmag and mr
Definition of P as material property in terms of electrical dipole moment m and density NV | P = <m> · NV | J = <m> · NV | Definition of J as material property in terms of magnetic moments m and density NV
|  | M = J/m0 | Definition of magnetization M
|  | M = cmag · H | Relations between M and H

| Next, let's compare mechanisms that lead to polarization
Dielectric Polarization | Magnetic Polarization
Electronic polarization |  |  | Diamagnetism
Induce dipole moments by displacing electrons and nuclei. Weak for spherical atoms. Stronger for covalent bonds. Important for optics. | er » 1,0001 .... 30 | mr » 0,9999 | Induce precession of electrons. Always very weak and opposite to field. Not important.
Orientation polarization |  |  | Paramagnetism
Average small orientation of fluctuating existing dipoles. Only in liquids; can be large. Not important. | er » 2 ..... 100 | mr » 1,0001 | Average small orientation of existing dipoles free to rotate in solids. Always small; not important. Extreme case: Ferromagnetism.
Ionic polarization |  |  | No direct counterpart
Net dipole moment from distribution of charges. Important. | er » 2 ... 100 |  |
Ferroelectricity Natural dipoles defined by crystallography are lined up. Important. | er > 1000 | mr > 1000 | Ferromagnetism Natural magnetic moments are lined up in any directions (with crystal directions preferred). Extremely important.

With frame

4.1.1 Magnetic Materials

© H. Föll (Advanced Materials B, part 1 - script)