Magnetics Business & Technology - July/August 2024 - 30

TECH TIPS
Understanding the Different Kinds of Magnetic Properties
Electric dipole (left) and magnetic dipole (right). While electric dipoles can be isolated to a pair of point charges of opposite sign, no one
has ever isolated point sources of magnetic north or magnetic south. No matter how many times you cut a permanent magnet in half,
you end up with two smaller permanent magnets.
Depending on how they interact with magnetic fields, most materials
are classified as diamagnetic, paramagnetic, ferromagnetic,
ferrimagnetic, or antiferromagnetic. We love the article
by Mike Gedeon, customer technical services manager of Materion
Performance Alloys and Composites, that explains these
different kinds of magnetic properties and related aspects such
as magnetic susceptibility. A few highlights follow.
Dielectric materials have electric dipoles, which are atoms or
molecules with positive and negative charges at opposite ends.
The number and behavior of these dipoles determine the dielectric
properties of the material. Materials also have magnetic
dipoles, which determine their magnetic properties. Magnetic
materials are often subdivided into regions where the dipoles
tend to share the same alignment. These regions are known as
domains, and there may be many such domains within a single
crystalline grain within the material.
In a magnetic material, the magnetic moment arises from the
magnetic field generated by the spin of the electrons. (Strictly
speaking, the magnetic moment is the torque generated as the
dipoles try to align themselves with or against the magnetic
field.) In a dielectric material, the electric dipole moment arises
from the electric field created between the positively charged
end and the negatively charged end.
While the electric dipole is produced by pairs of point charges
(a positive electric monopole and a negative electric monopole),
there has been no corresponding magnetic point charge
(magnetic monopole) found to date, although some researchers
are looking for therm. While electric field lines loop be30
Magnetics Business & Technology * July/August 2024
tween and around a pair of point sources, magnetic field lines
loop around a single point source, as depicted in the figure
above. For the sake of completeness, he notes that an electric
current travelling around a closed loop also creates a magnetic
dipole, but this field does not arise from an intrinsic material
property and disappears when the current is turned off.
Magnetic permeability (μ) describes how materials respond to
an applied external magnetic field. Often, it is expressed as
a relative magnetic permeability (μr), which is the ratio of the
material's magnetic permeability to that of frees pace. When a
dielectric material is placed in an electric field, the electric dipoles
in the material change the effective field strength. In the
same way, magnetic dipoles in materials interact with applied
magnetic fields to change the field strength within the material.
If the dipoles align with and strengthen the external field, the
relative magnetic permeability is greater than 1. If the dipoles
align to oppose the applied magnetic field, the relative permeability
is less than 1. If the field passes through the material
completely unaffected (the material is magnetically transparent),
then the relative permeability is exactly equal to 1.
Gedeon goes on to explain the distinctions of ferromagnetic
materials, antiferromagnetic materials and ferrimagnetic materials.
Plus, you can see a fascinating video.
Look for his series " In Our Element " at www.materion.com.
Based in Mayfield Heights, Ohio, Materion is an advanced
materials supplier that, among its portfolio, manufactures highpurity
magnetic alloys for thin film deposition.
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Magnetics Business & Technology - July/August 2024

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