How do you charge magnets?
Answer:
You place them in a very strong fixture that has a very powerful electromagnet inside and you pulse the electromagnet with a very high current, this pushes the magnetic material far into what is called saturation and charges it up. The fixture has to be designed for the specific shape of magnet involved.
Here is an example:
http://www.allmagnetics.com/device/magne...
You will occasionally find these magnetizer units offered for sale on ebay for pennies on the dollar.
If it's a permanent magnet you can increase it's
magnetism a little bit by leaving it attached to a more powerful one for a while. If it's an electro magnet you charge it by increasing the DC current flow through it's windings.
A good permanent magnet is made of a high coercivity alloy. That means it's hard to magnetise and hard to demagnetise. They're made by heating the bar of metal to a temperature higher than its curie point; the temperature above which it loses its magnetism, which typically is a few hundred degrees Celsius. Then you put it inside a strong magnetic field, provided by a coil through which a heavy direct current is passed, and allow it to cool. It retains the magnetic field. These days there are some very powerful high coercivity alloys made by alloying ferromagnetic metals like iron, cobalt and nickel with rare-earth metals like samarium and neodymium.
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