- Issue Time
- Jul 27,2019
We generally see two main types of rare earth magnet in use today, neodymium magnets and samarium cobalt magnets. They both come in different grades and have different properties and applications. Neodymium magnets, the stronger of the two, use an alloy that contains mainly neodymium, iron, boron, and varying degrees of dysprosium and praseodymium.
Rare earth magnets have become a common feature in the world of power tools. But have you ever wondered what differentiates them from regular, run-of-the-mill magnets? Some of you probably already know the difference, but, for those of us who haven’t been all that concerned about learning any better, the term “rare earth magnets” can sound like fancy marketing jargon that doesn’t have any real importance in how a tool actually functions. The term makes it sound like Klein, for instance, might’ve drilled down to the molten core of the earth to extract the materials to make the magnet for my new tape measure. But, is the mythical-sounding rare earth magnet even all that complex or rare? Well, we got tired of wondering, and looked into it ourselves.
Some folks have posited that magnetic force is miraculous. While that can be forgiven, as the nature of the magnet does seem mysterious, the explanation for magnetic force has been definitively laid out in most junior high school classes across the country. Which is to say that, while magnets are pretty cool, calling them “miraculous” is probably playing a bit too fast and loose with the term.
But, for the sake of having a refresher, and without getting too deeply scientific about any of it, here are the basics: matter is made up of atoms. At the center of the atom, we have a nucleus consisting of protons and neutrons. Orbiting the nucleus, much like satellites orbit the earth, we have tinier particles called electrons. The movement of electrons generates a magnetic field.
Most electrons travel in pairs that orbit in opposite directions, canceling out any magnetic force that their movement generates. The thing is, in some matter, like iron, atoms may have unpaired electrons which produce net magnetic fields that turn the whole atom into a tiny magnet.
Of course, magnetism, as a subject, is far more vast than we’re able to cover on this page. For the time being, however, this action describes why ferromagnetic (“magnetic like iron”) materials attract one another.
So, what is a rare earth magnet? Basically, they’re just like your regular ol’ run-of-the-mill magnets, except stronger. Rare earth magnets are the strongest type of permanent magnets available right now. Take your standard ferrite or alnico magnets, for instance. They typically generate a magnetic field of around .5 to 1 Tesla (the unit for measuring magnetic fields). Rare earth magnets punch in at around 1.4 Teslas and can generate even higher magnetic fields.
The term “rare earth” is also a bit of a misnomer. Rare earth elements, coming from the lanthanide, scandium, and yttrium families of the periodic table, are actually fairly abundant. They are, however, rarely found in large, concentrated deposits, but dispersed among other elements. From there, magnet manufacturers use these elements in the alloys that form rare earth magnets.
We generally see two main types of rare earth magnet in use today, neodymium magnets and samarium cobalt magnets. They both come in different grades and have different properties and applications. Neodymium magnets, the stronger of the two, use an alloy that contains mainly neodymium, iron, boron, and varying degrees of dysprosium and praseodymium. Because these magnets tend toward brittleness and are vulnerable to corrosion, manufacturers typically coat or plate them to protect from breaking and chipping.
Samarium cobalt magnets are the older of the two types. They are made from an alloy containing samarium, cobalt, iron, copper, hafnium, zirconium, and praseodymium. Typically difficult to demagnetize, samarium cobalt magnets have high operating temperatures and high resistance to corrosion.
Both of these rare earth magnets find use in a variety of applications these days. Computer hard drives, various engine designs, MRI machines, fishing reel brakes, toys, and even guitar pickups all use rare earth magnets. They’re incorporated into all sorts of other applications as well.
Brushless motors seem to make the world go ’round these days, and they have rare earth magnets to thank. Rather than metal brushes making contact with the motor, the brushless motor sort of turns the whole engine inside out. Permanent rare earth magnets are mounted to the rotor, and as electricity runs to the magnets, the polarities of the magnets drive the shaft. Brushless motors tend to be more precise, quieter, more durable, cooler-running, and more powerful than brushed motors. Thanks, rare earth magnets!
So, while it’s a little disappointing that rare earth magnets are not actually forged in the fires of Mordor like their name might suggest, they’re actually instrumental in making today’s cordless tool technology possible. Thankfully, the “rare” designation is more like an ironic nickname than anything else, because finding these elements with such regularity helps drive a lot of new innovation.