Everything about Neodymium Magnet totally explained
A
neodymium magnet or
NIB magnet (a variety of
rare-earth magnet) is a powerful
magnet made of a combination of
neodymium,
iron, and
boron — Nd
2Fe
14B.
Description
Neodymium magnets are very strong relative to their mass, but are also mechanically fragile. Like other
ferromagnetic materials, neodymium magnets lose their magnetism above a temperature known as the
Curie point. But the most powerful grades lose their magnetism at a relatively low temperature: 80 degrees
Celsius (176 degrees
Fahrenheit) and above. High-temperature grades will operate at up to 200 and even 230°C but their strength is only marginally greater than that of a
samarium-cobalt magnet.
As of 2008 neodymium magnets cost $50.00/lb, $1.40 per BHmax.
Range of strength
Neodymium magnets (or “neo” as they're known in the industry) are graded in strength from N24 to the strongest, N54. The theoretical limit for neodymium magnets is grade N64. The number after the N represents the magnetic energy product, in megagauss-oersteds (MGOe) (1 MG·Oe = 7,958·10³ T·A/m = 7,958 kJ/m³). 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 one requires about 18 times as much
ceramic magnet material for the equivalent magnet lifting strength, and about 3 to 5 times as much for the equivalent dipole moment.
Uses
They have replaced marginally weaker and significantly more heat-resistant samarium-cobalt magnets in most applications, due mainly to their lower cost.
Used for stabilization and angular head
motors in computer
hard drives, neodymium 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 for students to see the effects of
Lenz's Law in non-ferrous metals may be performed by dropping a strong neodymium 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 many
headphones. Neodymium magnets are becoming increasingly common in
loudspeakers for high-volume
sound reinforcement applications.
Neodynium magnets have been used several times before on the
Discovery Channel television show
Mythbusters in myth tests using magnetism where conventional magnets were not powerful enough. A series of 13 very large magnets of this type were proven to be able to drastically alter the .
Toys
As NIB magnets produced in
China have become less expensive in the last few years, the toy industry has used millions of them in magnetic building sets and other products including magnetic jewelry.
Marky Sparky Toys
uses them in their Magnetic Dart Boards, Rose Art Industries of
New Jersey, now owned by
Mega Brands, Inc. of
Montreal,
Canada, manufactures a popular line of
Magnetix and
Magna Man toys containing neodymium magnets the size and shape of aspirin tablets. The small cylindrical magnets are used at the ends or corners of plastic pieces in order to allow connections of multiple pieces. The
Magnetix brand was the subject of a March, 2006
recall notice by the
Consumer Product Safety Commission as well as numerous consumer lawsuits due to product safety concerns. In defective kits the NIB magnets became dislodged from their plastic housing, and many children of varying ages consumed the small magnets; see health hazards below.
Further development
The neodymium magnet industry is continually working to push the maximum energy product (strength) closer to the theoretical maximum of 64 MGOe. Scientists are also working hard to improve the maximum operating temperature for any given strength.
Health hazards
Neodymium magnets should always be handled carefully. Some that are slightly larger than the size of a
penny are powerful enough to lift over 10 kilograms. Strong magnetic fields can disrupt the operation of some internal medical devices such as pacemakers. While most solid state electronic devices are not affected by magnetic fields, some medical devices are not manufactured to mitigate the effects of strong magnetic fields. These design flaws can be hazardous to patients using these devices. If swallowed, neodymium magnets can cause lethal conditions by joining up inside the intestine.
An NIB's magnetic force increases with the size of the piece of
ferromagnetic metal, larger neodymium magnets can severely pinch skin or fingers, or even break bones when suddenly attracted to a magnetic object. Operating a large neodymium magnet close to smaller magnetic objects (keys, pens, etc.) and larger magnetic surfaces (radiator or a car, for example) can be dangerous if the person is caught between the magnet and the magnetic object or surface.
Neodymium magnets are made with special powders and coatings, so they're very fragile. They are often plated with a metal such as
nickel. The magnets can
fracture at
temperatures over 150 °C, or under impact as a result of their own acceleration. When this happens, in some cases the magnets may break apart so suddenly that flying pieces can cause injury. Some magnet suppliers have started providing NIB magnets optionally encased in plastic or rubber to decrease the possibility of injury and breakage due to impact.
Other dangers
Caution must be taken when using neodymium magnets. A neodymium magnet is powerful enough to destroy the contents of a
floppy disk to such an extent that the information is unrecoverable, a guarantee not present with techniques such as
formatting the disk. In addition, neodymium magnets are one of the only materials that can successfully erase the information contained on the magnetic stripes of
credit cards. Neodymium magnets are often strong enough to not only magnetize color
CRT metal
shadow masks, but also physically deform the mask itself. Such damage is typically not repairable by
degaussing.
Physical and mechanical properties
Further Information
Get more info on 'Neodymium Magnet'.
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