Neodymium magnets are a type of permanent magnets also known as rare earth magnets, due to the fact that they contain one or more of the rare earth elements of the periodic table. Most are made of a metal alloy containing neodymium, iron, and boron. They are much stronger than most of the magnets people are accustomed to using, like refrigerator magnets. Because of the forces they generate, they can be dangerous or even cause fatal injury if not handled properly.
These magnets are the strongest permanent magnets available, and are able, in some cases, to hold up more than 1,000 times their own weight. They are manufactured in many different shapes and sizes, such as cubes, discs, spheres, plates, and rings, among others. Small ones are used in certain electronic devices, such as computer hard drives and headphones. They have also been found to be useful in the construction of engines for remote-controlled model aircraft.
The strength of neodymium magnets is noted as the letter "N" followed by a number, with a range from N24 to N55. In theory, it is possible to make one that is as strong as N64, but this remains a mostly theoretical possibility. These magnets have some odd properties when they interact with certain other materials because of their impressive strength-to-size ratio.
One of these properties is known as magnetic braking, and it can be observed by dropping a neodymium magnet through a copper pipe. The magnet's fall will be very slow, because of the way that the magnet and the nonmagnetic copper interact with each other. Immersing the copper pipe in liquid nitrogen is said to enhance this effect. A row of sufficiently strong neodymium magnets is powerful enough to affect the speed and angle of a steel bullet in flight.
Most of the neodymium magnets in use are small, and even these can be dangerous if improperly handled. For example, if a child is left unattended and swallows two small magnets, they can pinch together internal organs and cause fatal injuries or infections. Even more care must be taken with larger magnets, such as those that are as large as the palm of a person's hand. These magnets are strong enough to affect everything magnetic or electronic in a room, often with unpleasant results.
Manufacturers are unable to ship these larger magnets on aircraft, because they are so strong that they can interfere with a plane's navigation system, especially its compass. The websites of many neodymium magnet retailers are replete with safety warnings regarding their handling. Despite these warnings, the magnets can prove very useful in scientific applications, both for demonstration and experimentation.