<P> 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 (Nd Fe B), 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 holddowns, 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 . </P> <P> 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 . </P> <P> 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 . There have even been cases where 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 . </P> <P> The U.S. Consumer Product Safety Commission passed a rule restricting rare - earth magnet size in consumer products, but it was vacated by a US Federal court decision in November 2016 . </P>

What are rare earth magnets made out of