TYPES OF MAGNETIC MATERIALS Diamagnetic Materials Paramagnetic Materials Ferromagnetic Materials
TYPES OF MAGNETIC MATERIALS
All materials are affected by magnetic fields. Matter is made up
of atoms with a positively charged nucleus surrounded by a field or
cloud of negatively charged electrons. The electron field is in
continual motion, spinning around the nucleus. When the material is
subjected to a magnetic field, the electron orbits are slightly
distorted. The amount of this distortion ( or the corresponding change
in magnetic characteristics) when subjected to an external magnetic
field provides a means of classifying materials into three groups:
diamagnetic, paramagnetic or ferromagnetic.
The term diamagnetic refers to a substance with magnetic
permeability slightly less than that of a vacuum. When placed in a
strong magnetic field, their induced magnetism is in a direction
opposite to that of iron. Diamagnetic materials include mercury,
gold, bismuth and zinc.
Paramagnetic denotes a substance with permeability slightly
greater than that of air. When such materials are placed in a strong
magnetic field, there is a slight alignment of the electron spin in the
direction of the magnetic flux flow. This alignment exists only as
long as the paramagnetic material is in the external magnetic field.
Aluminum, platinum, copper and wood are paramagnetic materials.
Ferromagnetic materials have a permeability greater than that of
air. When placed in an external magnetic field, the magnetic
domains align parallel with the external field and remain aligned for
some period of time after removal from the field. This continued
alignment after removal from the external field is called retentivity.
It can be an important property in some magnetic particle testing