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Magnetic Moment of a Rare-Earth Magnet?

  1. Aug 6, 2011 #1
    I was trying to find the value of the magnetic field at a distance x from a rare-earth magnet and came across this equation:

    [itex]B=\mu_o*2\mu/(4\pi*d^3)[/itex]

    Does anyone happen to know the magnetic moment, [itex]\mu[/itex], of a rare-earth magnet? Nothing specific, an order of magnitude value is fine.

    Thank you!
     
  2. jcsd
  3. Aug 7, 2011 #2
    For a neodymium magnet that has permeability near 1 and produces around 1.1T in short-circuit, you could:
    multiply its volume by 1.1T/(4pi*10-7)
    that is, volume * 875kA/m.

    With neodymium, this approximation is not bad. True data there for instance:
    http://www.cy-magnetics.com/CY-Mag-NdFeB.pdf
    remember 1 G = 100 µT and 1 Oe produces 1 G in vacuum. These were the CGS units.

    AlNiCo magnets, as well as iron magnets, have an important permeability, so you can't convert their short-circuit induction to the coercivity as if they were vacuum plus a coil. But with ferrite magnets, the approximation holds more or less.
     
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