Mad about Science: Magnets

By Brenden Bobby
Reader Columnist

Paraphrasing the internet subculture of my heyday: Freaking magnets, how do they work?

Magnets are objects that produce their own magnetic field and attract ferromagnetic materials such as iron, steel and cobalt.

Despite some similarities, gravity and magnetism are two very different forces. Both are invisible forces, but gravity acts as an attractor, while magnetism can both attract and repel. Try to push two magnets together with opposing magnetic poles and they will fiercely resist you. If you were to try that with two massive celestial bodies with gravitational pull, they would collide and destroy one another.

Confusingly, very large celestial bodies will exert forces of both gravity and magnetism. The Earth has a magnetic field, which is why your compass will point northward. This magnetic pole is created by huge quantities of liquid iron and nickel moving in the Earth’s outer core. These vast quantities of molten ferromagnetic metal create a powerful magnetic field many times the size of Earth.

The Earth isn’t the only celestial body with a magnetosphere. The sun has numerous magnetic poles created by similar processes. Rather than iron and nickel being the primary generators, the sun’s magnetic fields are created by vast quantities of plasma emerging from the sun itself. This can be viewed through special cameras and telescopes as huge arcs many hundreds of times larger than Earth. Sometimes these bands appear to “snap” when the sun’s various magnetic poles shift. When this occurs, it flings huge amounts of plasma and intense magnetic fields into space. This is called a coronal mass ejection, and it can cause intense auroras and even power outages when they impact Earth.

The reason we only see an aurora at northern and southern latitudes has everything to do with the Earth’s magnetosphere. Normally, our magnetosphere does a great job of deflecting magnetic interference from space. A small (cosmically speaking) amount of electromagnetically charged material is able to follow the magnetic field lines and impact gases in our atmosphere, which causes them to glow green and red. It’s sort of like water finding a crack in a rock and getting stuck inside that rock for millions of years. These lines lead to the north and south poles of Earth, which creates the aurora borealis and aurora australis, depending on which hemisphere you happen to be standing.

Artificial magnets work essentially the same way as the magnets described above, but at a much smaller scale. Most magnets we see now are neodymium magnets. Neodymium magnets are made from an alloy of the elements neodymium, iron and boron. During the production process, the neodymium alloy is exposed to a powerful magnet that aligns the magnetic poles within the structure to create an intense magnetic field. Magnetic poles in most structures are randomly aligned to create weak fields, but unified poles in structures create much stronger fields.

The primary power of neodymium magnets comes from the interaction between neodymium and iron. Neodymium forms an organized crystalline lattice structure that strengthens the magnetic field generated by the iron. The boron stabilizes the structure and keeps the magnets stable, aligned and powerful.

At-home magnets don’t require an active electrical current to generate a magnetic field. Larger magnets used for industrial purposes will employ an electrical current, as it can amplify the strength of the field many thousand times over. This is most commonly seen in scrapyards with large industrial magnets. These crane-hoisted magnets work by having a soft iron core that is encapsulated by coils of copper wire. When electrons are run through the copper wire, they create an electromagnetic field that aligns the iron to create a very strong pull. As soon as the current stops, the magnetic field reduces, too.

Forces like these are great for lifting huge chunks of metal that weigh several thousand pounds. Cars and appliances are the primary purpose for these powerful crane magnets, but they work just as well to pick up clusters of loose ferrous detritus as well.

CERN uses a similar principle for the Large Hadron Collider, but with some extra steps involved. CERN uses niobium-titanium cables cooled to -271.3 degrees Celsius, making them a superconductor. A superconductor has zero electrical resistance for electrons passing through the structure and creates a magnetic field when cooled below a certain temperature. This is also used in MRI machines, but the LHC is an application of this process on a gigantic scale. 

Maglev trains also function this way. By creating powerful repelling fields using powerful superconductors, the trains are able to levitate off the track to reduce a primary source of friction. Friction causes a loss of efficiency for traveling objects as well as increasing the amount of wear and tear on the train. Maglev trains have much higher production costs but vastly lower maintenance costs. Additionally, they are extremely fast, with the fastest being Japan’s SCMaglev capable of reaching 375 miles per hour!

Stay curious, 7B.