Learning is all about asking questions, and no one asks questions better than children. Boise State is home to more than 1,400 faculty members and researchers who are eager to answer these amazing questions.
Today, materials scientist Peter Mullner answers a child’s question about magnets: ‘What are magnets made of, and how do they work?’
At Boise State, Mullner oversees the Magnetic Materials Lab and he has studied magnets for 25 years. He researches “smart magnets” from which his lab invented a supercool micropump and rare-earth-element-free magnets, which may help with developing green technology. He has authored over 200 scientific publications and 13 patents.
Question: What are magnets made of?
Let’s start with learning a new word: Ferromagnetism.
The word “ferro” comes from the Latin word ferrum, which means iron, said Mullner. That’s why “Fe” is the symbol for the chemical element iron. Most of our magnets are made of iron as a metallic alloy (an alloy is a metallic substance composed of two or more elements), but also as it appears in minerals. For example, iron is in the mineral ‘magnetite’. Magnetite was one of the first magnets that humans discovered.
Most of our magnets are still largely made of iron, but a regular piece of iron is not a strong magnet. You can magnetize it by placing it near a strong magnet, but it quickly loses its magnetic strength when you remove the strong magnet.
To make stronger magnets, we add rare earth elements!
Question: How do magnets work?
To understand how magnets work, we have to look inside of the materials that they are made of.
Inside the material, we find the smallest building blocks — atoms. If you chop up iron smaller and smaller, eventually you get to an iron atom, which is the smallest indivisibly tiny piece of iron.
These iron atoms are like little magnets. Just like magnetic toys — let’s say, rods and spheres — you can align them end to end, and all the little magnets point in the same direction, making a strong magnetic rod.
But if you put two rods side by side with matching poles together (like head to head and tail to tail), they repel each other. If you arrange them head to tail, they stick together. By sticking together in this way, the overall structure loses much of its magnetic strength. Hold it to another magnet, and you won’t feel much attraction.
You can create entire cubes of magnets arranged this way, but they won’t feel other magnets from the outside. This is similar to what happens inside iron. If not prevented, the tiny magnetic atoms flip around and form different small areas pointing in different directions. These are called magnetic domains. If these domains point in different directions, the whole piece of iron loses its magnetic strength. We call this process demagnetization.
How can we prevent demagnetization? Can we force the atomic magnets to align and stay aligned?
For super strength, we add rare earth elements
The answer to the last question is yes. To make really strong magnets, we mix iron with other elements like neodymium and boron, especially the so-called rare earth elements – like dysprosium and neodymium – which are good at adding strength to magnets when added in the right amount.
These elements do exactly that, they force atomic magnets to align and stay aligned. It doesn’t take much of these elements, but without them, the magnets don’t work for what we need them. These magnets don’t just hold papers to your fridge. They work in things like cars, phones, wind turbines, medical devices and fighter jets.
We measure the strength of a magnet through its “energy product”. The higher the energy product, the more difficult it is to demagnetize the magnet. For example, one strong magnetic alloy (a material made by adding two or more metals together) is made from neodymium, iron and boron: this mix makes a Ne-Fe-B magnet.
One Ne-Fe-B magnet about the size of a dime can hold around fifteen pounds of iron to a steel beam! You find several tons of these magnets in the generator of a wind turbine. Because they are so strong, we can also use them in very tiny amounts, for example to make a cell phone buzz and control the read/write function of a computer hard drive.
But we can’t use a neodymium, iron and boron magnet for everything. Alloys have specific properties that make them work really well in some situations, but not so well in others.
For example, a different type of rare-earth magnet is used in the F-35 fighter jet. Ne-Fe-B magnets don’t work for fighter jets because these jets get hot and Ne-Fe-B loses its magnetic strength at moderate temperature.
Magnets made of samarium and cobalt (Sm-Co) are not quite as strong as Ne-Fe-B but they can sustain much higher temperatures without losing their magnetic strength.
In short, the way a magnet will be used ultimately defines what materials go into it! And figuring that out can be the exciting job of a materials scientist.
Further Viewing for Kids:
PBS Curious Crew: Learn with other kids about the power of Magnetism
Further Reading for Adults:
The American Geosciences Institute: What are rare earth elements, and why are they important?
How the US can mine its own critical resources without digging new holes.
From glass and steel to rare earth metals, new materials have changed society throughout history.
National Geographic on magnetism.
The Energy Transition Will Need More Rare Earth Elements. Can We Secure Them Sustainably?
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