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.
     
     

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