Magnetic materials properties
All materials show some magnetic effects. In engineering, taking by definition r = 1 for a free vacuum, materials are divided into two main groups:
- Non-magnetic materials - r 1
From the physics course it is also known that non-magnetic materials are divided in addition into diamagnetics
(such as copper, silver, lead), where r < 1, and
paramagnetics (such as air, aluminium) where r > 1.
But of main interest are the so-called ferromagnetics (such as iron, nickel, cobalt and their alloys), where r
may reach value of several thousand.
Due to the spinning of the electrons and their orbital movement around the atom nucleus, a vector quantity "magnetic moment m" is introduced as product of the electron micro current and the area enclosed by the electron orbit;    In figure (b) a result is presented when a strong external field H is applied in direction from left to right. As seen all the domains magnetic moments have aligned into external field H direction. Such condition for the iron is called "saturation". It means that the magnetic flux density B inside the material could increase over again only on account of additional external field applied.
It should be noted that above certain temperature called "Curie point", alignment of domains is totally destroyed, which results in the fact that material looses its magnetic properties. For the iron this temperature point is 770oC.    Magnetization of materials in the presence of external field is called induced magnetization. It differs from the permanent magnetization which is present in absence of external field. Materials exerting permanent magnetization are called permanent magnets.
Electromagnetic Module. Modelling, Analysis and Design.
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