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.
TGD stock 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 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.
Very Powerful pull for the size
Can 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
Ferrite magnets are manufactured from iron oxide Fe203 black rust with additives of strontium. Specialized machining techniques must be used to machine this material. Un-magnetized magnets can be cut by straight cuts using diamond blades; this is known in the trade as “slice and dice” process.
The corrosion resistance of Ferrite is considered good, and no surface treatments are required.
However, Ferrite magnets may have a thin film of fine magnet powder on the surface and for clean, non-contaminated applications; some form of coating may be required.
Anisotropic grades are oriented in the manufacturing direction, and must be magnetized in the direction of orientation. Another word for orientated would be pre-magnetized.
Isotropic grades are not oriented and can be magnetized in many different ways, although some degree of greater magnetic strength will be found in the pressing dimension, usually the shortest dimension.
Ferrite magnets are normally magnetized at the factory in the course of manufacture.
Limited magnetizing of un-magnetized magnets can be processed locally, but only to the direction of orientation.
Safety precautions should always be taken in consideration when handling these magnets.
Ferrite magnets can be used up to 250 degrees Celsius, although there is a loss of magnetism with the increase of temperature. Beyond 250 degrees Celsius one reaches a point, the so called, cure temperature where the loss in magnetism is not self-generating and the magnets would require re-magnetizing.
Ferrite magnets are widely used in motors, magnetic couplings, for sensing, loudspeakers, holding-magnet systems, crafts, magnetic therapy, novelties, and toys.
Metal Alloy / AlNiCo
Metal Alloy magnets are normally cast in a foundry process, but are sometimes sintered. There are many magnet alloys comprising different proportions of aluminium, nickle and cobalt which create different magnetic characteristics.
Also called AlCoMax3 or AlNiCo due to the elements Aluminium(Al) Nickle(Ni) and cobalt (Co)
Alnico is the most widely used high quality magnet alloy. Metal alloy magnets have high working temperatures in the region of 450°C and they are mechanically stronger than any other magnet material. Metal alloy magnets are normally anisotropic, being magnetized through the longest dimension "L" and as a result they have a "long throw" of magnetic field making them ideal for use with remote reed switches and hal effect sensors for proximity indication and switching. There are a variety of finishes available for metal alloy magnets with as-cast finish being the cheapest which is normally acceptable for industrial use. Ground execution is an option where finer dimensional tolerances are required and so-called laboratory magnets normally have a painted finish. Bar and rod shapes are used extensively.