什么引起一些材料带磁性。

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What causes some materials to be “magnetic”?
什么引起一些材料带磁性。
The origin of magnetism lies in the atomic structure of the elements that make up the material. All atoms
have electrons that spin in discrete orbits around a nucleus. Since electrons can be represented as electrical
charges in motion, they produce a weak magnetic field. In most elements, electrons act in pairs with
equal and opposite moments, so the weak electromagnetism is canceled out, however a few elements have
electron orbits which are not paired, and which align in the same direction producing a very weak magnetic
bulk effect.

Ferromagnetism, a property of only a few metals such as iron, nickel, cobalt and manganese, is a bulk effect
where large numbers of atoms group together and combine their spin moments so that they are aligned in
the same direction. These regions may contain as many as 1014 atoms, and are called magnetic domains.
The atomic alignment tends to decrease as temperature increases, until a temperature is reached called
Curie point, at which ferromagnetism ceases.

When the magnetic domains are aligned and locked within the crystal lattice, the material retains a “permanent”
magnetic state, and will attract or repel other ferromagnetic material. If the domains are not locked
within the lattice, the material will be attracted to “permanent” magnets, but will retain little or no magnetism
itself. Materials that have the property of ferromagnetism “conduct” magnetic flux in a manner similar to that
in which electrical conductors carry electricity.

Ferrites are more complex than bulk metals. There are oxygen atoms as well as metal atoms in the ferrite
crystal lattice, and these interact in a manner called ferrimagnetism. In a bulk sense, they form domains
similar to ferromagnetic materials, but they retain special properties that are unique to ferrites, such as high
resistivity and in the case of soft ferrites, very low retentivity. These properties make them ideally suited to
use in impeders.