Neodymium magnet
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Image:Neodymag.jpg A neodymium magnet (also, but less specifically, called a rare-earth magnet) is a powerful magnet made of a combination of neodymium, iron, and boron — Nd2Fe14B. These magnets are very strong in comparison to their mass, but are also mechanically fragile and lose their magnetism at temperatures above 80 degrees Celsius. They have replaced marginally weaker and significantly more heat-resistant samarium-cobalt magnets in most applications, due mainly to their lower cost. They are graded in strength from N24 to the strongest N54. The number after the N represents the magnetic energy product, in megagauss-oersteds (MGOe) (1 MG·Oe = 7,957 T·A/m = 7,957 J/m³) . There is constantly work to increase the power until a limit of about N60 will be reached. N48 has a remnant static magnetic field of 1.38 teslas and an H (magnetic field intensity) of 13,000 oersteds (1.0 MA/m). By volume it requires about 18 times as much ceramic magnet material for the equivalent magnet strength.
Image:Neodymium magnet lifting spheres.jpg
Used for stabilization and angular head motors in computer hard drives, Nd2Fe14B magnets are also popular with hobbyists, and a small magnet can have amazing properties — it exhibits magnetic braking when moved near a non-magnetic metal due to induced eddy currents. An excellent demonstration to students of the eddy currents created in non-ferrous metals may be performed by dropping a strong Nd magnet through a copper pipe. The magnet will travel through the pipe remarkably slowly as it falls, the effect may be greatly enhanced by immersing the pipe in liquid nitrogen (thus increasing its conductivity even further) prior to dropping the magnet through. A somewhat larger magnet interacts strongly enough with the magnetic field of the Earth to allow its tendency to align with that field to be perceived directly when holding it, essentially forming a compass. Cylinder- and disc-shaped neodymium magnets are especially responsive to the Earth's magnetic fields. Neodymium magnets are used for the transducers in the earphones included with Apple's popular iPod music player, as well as in numerous other high-fidelity headphones or buds. Another recent use has been the inclusion of neodymium based magnetic pickups in the new Ernie Ball Musicman Bongo bass guitars.
Caution
However, caution must be taken when using neodymium magnets. Even a small neodymium magnet is powerful enough to destroy the contents of a floppy disc to such an extent that the information is unrecoverable, a guarantee not present with techniques such as formatting the disk. NdFeB magnets are often strong enough to not only magnetize color CRT shadow masks, but also physically deform the mask itself. Such damage is typically irreparable by degaussing.
Neodymium magnets should always be handled carefully. Some of the neodymium magnets that are slightly larger than the size of a penny are powerful enough to lift over 10 kilograms [1]. They are hazardous, being able to pinch skin or fingers when suddenly attracted to a magnetic object. Because they are made with special powders and coatings, the magnets are very fragile and break at temperatures over 150 °C, or if allowed to smash together. When they break, the magnets may break so suddenly that flying pieces may cause eye injury. Neodymium magnets should also be stored away from electrical appliances, magnetic (bank) cards and computer monitors, as damage may be irreparable.
See also
- Lanthanide series of rare-earth magnets LnFeB
- Transition metal substitutions like NdCoB
External links
- Rare-Earth Magnetics Association - Rare earth magnet informationja:ネオジム磁石