What are Rare Earth Magnets?
Rare-earth magnets are strong permanent magnets 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 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla.
Types of Rare Earth Magnets
Samarium–cobalt magnets (chemical formula: SmCo5/SmCo17), the first family of rare-earth magnets invented, are less used than neodymium magnets because of their higher cost and lower magnetic field strength. However, samarium–cobalt has a higher Curie temperature, creating a niche for these magnets in applications where high field strength is needed at high operating temperatures. They are highly resistant to oxidation, but sintered samarium-cobalt magnets are brittle and prone to chipping and cracking and may fracture when subjected to thermal shock
Neodymium magnets, invented in the 1980s, are the strongest and most affordable type of rare-earth magnet. They are made of an alloy of neodymium, iron, and boron (Nd2Fe14B), sometimes abbreviated as NIB. Neodymium magnets are used in numerous applications requiring strong, compact permanent magnets, such as electric motors for cordless tools, hard disk drives, magnetic hold-downs, and jewelry clasps. They have the highest magnetic field strength and have a higher coercivity (which makes them magnetically stable), but they have a lower Curie temperature and are more vulnerable to oxidation than samarium–cobalt magnets. Corrosion can cause unprotected magnets to spall off a surface layer or to crumble into a powder. Use of protective surface treatments such as gold, nickel, zinc, and tin plating and epoxy-resin coating can provide corrosion protection.
Originally, the high cost of these magnets limited their use to applications requiring compactness together with high field strength. Both the raw materials and the patent licenses were expensive. However, since the 1990s, NIB magnets have become steadily less expensive, and the low cost has inspired new uses such as magnetic construction toys.
Magnets4U (TGD) keeps stock of Neodymium Magnets, Samarium cobalt can be supplied upon request.
Rare Earth magnets are extremely brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from braking, chipping, or crumbling into powder.
The most popular plating is nickel coated.
The term “rare earth” can be misleading, as these metals are not particularly rare or precious; they are about as abundant as tin or lead. 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 magnetic energy product BHmax of neodymium magnets is about 18 times greater than “ordinary” magnets by volume. This allows rare earth magnets to be smaller than other magnets with the same field strength.
Common applications for Rare Earth Magnets
Rare earth magnets are widely used in computer hard disc drives, wind turbine generators, audio speakers / headphones, bicycle dynamos, magnetic resonance imaging devices, 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-cranked-powered) motion, industrial uses such as maintaining product purity, equipment protection, and quality control capture of fine metallic particles in lubricating oils.
Advantages of Rare Earth Magnets
- Very Powerful pull for the size
- Could be custom made with relatively small minimum order quantities
- Stable magnetism, not easily influenced by other magnetic fields
- Most popular magnet used in thousands of applications
- Available in different grading that influence strength and maximum temperature they are able to handle.
- Sizes are very accurate to the size specified, tolerance is normally 0.1mm