A rare-earth magnet is a strong permanent magnet made from alloys of rare-earth elements. Developed in the 1970s and 1980s, rare-earth magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as ferrite or alnico magnets. The magnetic field typically produced by rare-earth magnets can exceed 1.2 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla.
There are two types: neodymium magnets and samarium–cobalt magnets. Rare-earth magnets are extremely brittle and are vulnerable to corrosion, so they are usually plated or coated to protect them from breaking, chipping, or crumbling into powder.
The development of rare-earth magnets began around 1966, when K. J. Strnat and G. Hoffer of the US Air Force Materials Laboratory discovered that an alloy of yttrium and cobalt, YCo5, had by far the largest magnetic anisotropy constant of any material then known.
The term "rare earth" can be misleading, as some of these metals are as abundant in the Earth's crust as tin or lead, but rare earth ores do not exist in seams (as do coal or copper, for example), so in any given cubic kilometre of crust they are "rare". China produces more than any other country but it imports significant amounts of REE ore from Myanmar. As of 2025, China produces 90% of the world's supply of rare-earth magnets. Some countries classify rare earth metals as strategically important. Chinese export restrictions on these materials have led countries such as the United States to initiate research programs to develop strong magnets that do not require rare earth metals.
Properties According to Lucas et al, "To produce ferromagnetism and then a magnet the first condition is to select materials having a high concentration of paramagnetic atoms. A paramagnetic atom contains unpaired electrons, each of them being equivalent to a local magnet due to the orientation of the electronic spin." The RE sequence of metals are characterized by a gradual filling of the 4f level, resulting in a large number of unpaired electrons. For instance, neodymium has three unpaired electrons, while samarium has five. The resulting magnetic moment is due to the combined effects of spin and orbit. Yet, because RE metals have large metallic radii, their magnetic properties are limited on their own. They must be alloyed with transition metals such as Fe and Co, to produce a permanent magnet, especially if the magnetic dipoles align along a crystalline direction, called magnetic anisotropy. This anisotropy facilitates easy magnetization through dipole alignment, and difficulty with demagnetization, called coercivity. Both Fe and Co are very rich in unpaired electrons, ensuring strong magnetization.
Some important properties used to compare permanent magnets are: remanence (Br), which measures the strength of the magnetic field; coercivity (Hci), the material's resistance to becoming demagnetized; energy product (B·Hmax), the density of magnetic energy; and Curie temperature (TC), the temperature at which the material loses its magnetism. Rare-earth magnets have higher remanence, much higher coercivity and energy product, but (for neodymium) lower Curie temperature than other types. The table below compares the magnetic performance of the two types of rare-earth magnets, neodymium (Nd2Fe14B) and samarium–cobalt (SmCo5), with other types of permanent magnets.
Material Preparation Br(T) HCi(kA/m) (BH)max(kJ/m3) TC(°C) Nd2Fe14B sintered 1.0–1.4 750–2000 200–440 310–400 bonded 0.6–0.7 600–1200 60–100 310–400 SmCo5 sintered 0.8–1.1 600–2000 120–200 720 Sm(Co,Fe,Cu,Zr)7 sintered 0.9–1.15 450–1300 150–240 800 Alnico sintered 0.6–1.4 275 10–88 700–860 Sr-ferrite sintered 0.2–0.4 100–300 10–40 450 Iron (Fe) bar magnet annealed ? 800Introduction to Magnets and Magnetic Materials, David Jiles, Ames Laboratrories, US DoE, 1991 ? 770Beichner and Serway. Physics for Scientists & Engineers with Modern Physics. 5th ed. Orlando: Saunders College, 2000: 963Curie Temperature." McGraw-Hill Encyclopedia of Science & Technology. 8th ed. 20 vols. N.P: McGraw-Hill, 1997Hall, H.E and J.R. Hook. Solid State Physics. 2nd ed. Chichester: John Wiley & Sons Ltd, 1991: 226.
Types Neodymium
Neodymium permanent magnets were discovered in 1984. These strong permanent magnets are fairly cheap due to the lower cost of Fe versus Co, the abundance of Nd versus Sm, and the relatively little amount of Nd in the composition. The alloy of neodymium, iron, and boron (Nd2Fe14B) results in a strong uniaxial anisotropy tetragonal structure and a Curie temperature above room temperature. According to Lucas et al, "Examination of the Nd2Fe14B structure indicates that the solid can be described as a layer structure with alternate stacking sequences of a Nd-rich layer and a sheet formed only by Fe atoms. The boron atoms which are diamagnetic and nonmetallic do not participate in the magnetism but like C atoms in steel contribute to reinforce the cohesion of the material by strong covalent bonding."
Samarium–cobalt
Samarium–cobalt magnets, SmCo5 and Sm2Co17, are made of alloys consisting of a hexagonal structure and alternate layers of Co and Sm/Co. According to Lucas et al, "The result is a strong anisotropy leading to an easy magnetization along the c axis of the unit cell. The phenomena is enhanced due to the strong magnetic anisotropy of Sm atoms." These magnets have a high Curie temperature and maximum energy product, which warrants the higher cost.
Applications
Since their prices became competitive in the 1990s, neodymium magnets have been replacing alnico and ferrite magnets in the many applications in modern technology requiring powerful magnets. Their greater strength allows smaller and lighter magnets to be used for a given application.
Common applications of rare-earth magnets include:
Computer hard disk drives Wind turbine generators Loudspeakers / headphones Bicycle dynamos MRI scanners Fishing reel brakes Permanent magnet motors in cordless tools High-performance AC servo motors Traction motors and integrated starter-generators in hybrid and electric vehicles Mechanically powered flashlights, employing rare earth magnets for generating electricity in a shaking motion or rotating (hand-crank-powered) motion Industrial uses such as maintaining product purity, equipment protection, and quality control Capture of fine metallic particles in lubricating oils (crankcases of internal combustion engines, also gearboxes and differentials), so as to keep said particles out of circulation, thereby rendering them unable to cause abrasive wear of moving machine parts
Other applications of rare-earth magnets include:
Linear motors (used in maglev trains, etc.) Stop motion animation: as tie-downs when the use of traditional screw and nut tie-downs is impractical. Diamagnetic levitation experimentation, the study of magnetic field dynamics and superconductor levitation. Electrodynamic bearings Launched roller coaster technology found on roller coaster and other thrill rides. LED Throwies, small LEDs attached to a button cell battery and a small rare earth magnet, used as a form of non-destructive graffiti and temporary public art. Desk toys Electric guitar pickups Miniature figures, for which rare-earth magnets have gained popularity in the miniatures gaming community for their small size and relative strength assisting in basing and swapping weapons between models. Research on cancer treatment is exploring the use of magnetic nanoparticles(MNPs) made from rare earth metals. In magnetic hyperthermia, MNPs generate localized heat within tumor cells, leading to their selective destruction. In targeted delivery systems, MNPs are attached to therapeutics and guided by an external magnetic field to concentrate and retain them at the desired site.
Hazards and legislation
The greater force exerted by rare-earth magnets creates hazards that are not seen with other types of magnet. Magnets larger than a few centimeters are strong enough to cause injuries to body parts pinched between two magnets or a magnet and a metal surface, even causing broken bones. Magnets allowed to get too near each other can strike each other with enough force to chip and shatter the brittle material, and the flying chips can cause injuries. Starting in 2005, powerful magnets breaking off toys or from magnetic construction sets started causing injuries and deaths. Young children who have swallowed several magnets have had a fold of the digestive tract pinched between the magnets, causing injury and in one case intestinal perforations, sepsis, and death.
The swallowing of small magnets such as neodymium magnetic spheres can result in intestinal injury requiring surgery. The magnets attract each other through the walls of the stomach and intestine, perforating the bowel., Hamilton Spectator, March 13, 2013.Young kids can swallow magnets, seriously damage intestines, doctors warn Global News Toronto, March 12, 2013. The U.S. Centers for Disease Control reported 33 cases as of 2010 requiring surgery and one death. The magnets have been swallowed by both toddlers and teens (who were using the magnets to pretend to have tongue piercings).Feds file suit against Buckyballs, retailers ban product, USA Today, July 26, 2012.
North America
A voluntary standard for toys, permanently fusing strong magnets to prevent swallowing, and capping unconnected magnet strength, was adopted in 2007. In 2009, a sudden growth in sales of magnetic desk toys for adults caused a surge in injuries, with emergency room visits estimated at 3,617 in 2012. In response, the U.S. Consumer Product Safety Commission passed a rule in 2012 restricting rare-earth magnet size in consumer products, but it was vacated by a US federal court decision in November 2016, in a case brought by the one remaining manufacturer. After the rule was nullified, the number of ingestion incidents in the country rose sharply, and is estimated to exceed 1,500 in 2019, leading the CPSC to advise children under the age of 14 to not use the magnets.
In 2009 US company Maxfield & Oberton, maker of Buckyballs, decided to repackage sphere magnets and sell them as toys. Buckyballs launched at New York International Gift Fair in 2009 and sold in the hundreds of thousands before the U.S. Consumer Product Safety Commission issued a recall on packaging labeled 13+.Buckyballs® High Powered Magnets Sets Recalled by Maxfield and Oberton Due to Violation of Federal Toy Standard, Consumer Product Safety Commission, May 27, 2010. According to the CPSC, 175,000 units had been sold to the public. Fewer than 50 were returned. Buckyballs labeled "Keep Away From All Children" were not recalled. Subsequently, Maxfield & Oberton changed all mentions of "toy" to "desk toy", positioning the product as a stress-reliever for adults and restricted sales from stores that sold primarily children's products.Buckyballs Safety Compliance, Maxfield and Oberton.
In the United States, as a result of an estimated 2,900 emergency room visits between 2009 and 2013 due to either "ball-shaped" or "high-powered" magnets, or both, the U.S. Consumer Product Safety Commission (CPSC) has undergone rulemaking to attempt to restrict their sale.