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Rare Earth Magnets

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Rare Earth Magnets

A rare earth magnets is know as neodymium magnet, NdFeB magnet, NIB or Neo magnet, the most widely used type of rareearth magnet, is a permanent NdFeB magnet made from an alloy of neodymium, iron and boron to form the Nd2Fe14B tetragonal crystalline structure.

The advantage of the rare earth compounds over other magnets is that their crystalline structures have very high magnetic anisotropy. This means that a crystal of the material is easy to magnetize in one particular direction, but resists being magnetized in any other direction.

Atoms of rare earth elements can retain high magnetic moments in the solid state. This is a consequence of incomplete filling of the f-shell, which can contain up to 7 unpaired electrons with aligned spins. Electrons in such orbitals are strongly localized and therefore easily retain their magnetic moments and function as paramagnetic centers. Magnetic moments in other orbitals are often lost due to the strong overlap with their neighboring electrons; for example, electrons participating in covalent bonds form pairs with zero net spin.

High magnetic moments at the atomic level in combination with a stable alignment (high anisotropy) of those atoms results in a high magnetic field strength.

Type are Samarium-cobalt and NdFeB Magnet

Samarium-cobalt magnets (chemical formula: SmCo5), the first family of rare earth magnets invented, are less used than neodymium magnets because of their higher cost and weaker 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 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.

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. Beginning in the 1990s, NIB magnets have become steadily less expensive, and the low cost has inspired new uses such as magnetic construction toys.

Application

  • computer hard disk 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
  • industrial uses such as maintaining product purity, equipment protection, and quality control
  • Linear motors
  • Stop motion animation as tie-downs when the use of traditional screw and nut tie-downs is impractical
  • Diamagnetic levitation experimentation, the study of magnetic field dynamics and superconductor levitation
  • Electrodynamic bearings
  • Launched roller coaster technology found on roller coaster and other thrill rides
  • LED throwies, small LEDs attached to a coin battery and a rare earth magnet
  • Neodymium magnet toys
  • Electric guitar pickups
  • Miniature figures, for which rare-earth magnets have gained popularity in the miniatures gaming community for their small size and relative strength assisting in basing and swapping weapons between models

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