Diamagnetism & levitation of pyrolytic graphite explanation

  • #1
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Hi,

This YouTube video shows various shapes of pyrolytic graphite suspended on an alternating polarity matrix of square neodymium magnets.


Diamagnetism-Pyrolytic-Graphite.jpg


As I understand the principle of diamagnetic anisotropy, the stronger the external magnetic force, the stronger the induced repulsive force in the diamagnetic material. Hence the levitation.

But the pieces of pyrolytic graphite are orientating to settle on the magnet matrix in a way that has maximum exposure to the interpole boundary between each magnet. To me this is counterintuitive, because this is where the magnetic field on the z plane (perpendicular to the surface) is weakest. It is strongest at the centre of the magnet.

With this logic (that’s obviously incorrect) the square and round graphite pieces should centre on a square magnet, not sit so as to gain maximum exposure to the boundary where the magnetic poles are alternating.

Am hoping someone who understands the phenomena can explain why the pyrolytic graphite orientates the way it does on this alternating magnetic matrix?

Thank you.
 

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  • #2
kuruman
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There are induced currents in the plane of the diamagnets that create a dipole moment perpendicular (normal) to the surface. If the normal to the surface is at an angle with respect to the magnetic field, there would be a torque that would restore the magnetic moment to be parallel to the surface. You can see the effects of the restoring torque in the video. When the diamagnets are bumped, the normal to the surface oscillates about the z-axis until the oscillations damp out.
 
  • #3
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Thank you kuruman, unfortunately not sure I follow. Might need a little more educating :)
You mention, where the magnetic field (from the magnet matrix) is at an angle, is this mainly along the boundaries between the opposing pole magnets?
That is, where the square magnets abut, the magnetic field strength on the z-axis would be near zero while being their strongest on the x-y plane.

Not sure how the torque restores the magnetic moment to be parallel to the surface?

Thanks in advance.
 

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