How Everything Works
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Question 1109

How are magnets made and what are they made of? — S, San Francisco, CA
The strongest modern magnets are made by assembling lots of tiny magnetic particles into a solid object. These magnetic particles are "intrinsically" magnetic, meaning that the atoms from which the particles are formed retain their magnetism in coming together as a solid. Electrons are naturally magnetic and most atoms exhibit the magnetism of their electrons. But as these atoms come together to form a solid, most of them lose their magnetism. For example, copper, aluminum, gold, and silver are all nonmagnetic solids built from magnetic atoms. There are only a few materials that don't lose their atomic magnetism and might be suitable for making permanent magnets. However, most of these magnetic materials only exhibit their magnetism when exposed to other magnets—when they're alone, their magnetism is mostly hidden. For example, iron and steel are magnetic materials but they only appear strongly magnetic when you bring a permanent magnet near them.

To make a strong permanent magnet, you must find a material that is both intrinsically magnetic and that is able to stay magnetic when it's by itself. Materials that hide their magnetism when alone do this by allowing their magnetic structure to break up into tiny pieces that all point in different directions. Each of these tiny magnetic pieces is called a magnetic domain, and iron and steel are normally composed of many magnetic domains. A good permanent magnet material is one that is intrinsically magnetic and that resists the formation of randomly oriented magnetic domains. A very effective way to make such permanent magnet materials is to assemble lots of tiny magnetic particles. Each of these particles is shaped in a way that makes one of its ends a north pole and its other end a south pole, and that makes it extremely hard for these two poles to exchange places. The particles are then aligned with one another and bonded together to form a permanent magnet. To make sure that the particles all have their north poles at one end and their south poles at the other end, the finished magnet is exposed to an extremely strong magnetic field—one so strong that it flips any misaligned magnetic particles into alignment with the others. After being magnetized in this manner, the permanent magnet is very hard to demagnetize, which is just what you want in a permanent magnet.

The most common magnet materials are Ferrite and Alnico. Ferrite magnets are made from a mixture of iron oxide and barium, strontium, or lead oxide. Alnico magnets are made from aluminum, nickel, iron, and cobalt, and consist of tiny particles of an iron-nickel-aluminum alloy inside an iron-cobalt alloy. But the strongest modern magnets are made from an iron-neodymium-boron alloy. The latter magnets are very resistant to demagnetization and the forces they exert on one another are amazingly strong.


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