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I Can you cancel part of a permanent magnet field by spinning?

  1. May 8, 2016 #1

    jfizzix

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    It's a random thought I had.

    Let's say you have a single perfect permanent magnet. There is just one magnetic domain, and the magnet is cut so that its magnetic moment is along a single crystal axis. For example, we can imagine a cube shaped magnet, with the magnetic moment pointing straight out the top face.

    My question is this:
    Has there been any experiment, where one rapidly spins such a magnet along the axis defined by its magnetic moment, and sees a measurable change in the magnitude of the magnetic field?

    Now I know you couldn't completely cancel out a permanent magnet just by spinning. The speeds needed would cause the magnet to fly apart. My question is whether any measured change in the magnetic moment has been shown, purely due to rotation. This would be a reversible change, since you could just stop the magnet spinning and see the field as it was before.

    Thoughts?
     
  2. jcsd
  3. May 8, 2016 #2
    side-question: why would spinning a perfectly cylindrical and symmetrically directed magnet affect its field at all? (i.e. excluding the time-variant effect of the cube's corners)
     
  4. Sep 18, 2016 #3

    jfizzix

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    The origin of the magnetism in the material is due to the angular momentum of the electrons surrounding each atom (oversimplifying, I know). If you spin the magnet in a direction opposite this angular momentum, the idea is that the total angular momentum, and therefore, the total magnetic field would be less.

    It makes sense that if we were in a reference frame orbiting the magnet about its axis, that the field detected would be different than if we were at rest with respect to the magnet. For example, if we had a loop of electric current, and we were orbiting the loop at sufficient speed so that the drift velocity of the charges appeared to be zero, we would detect no magnetic field in that reference frame.

    The only reason I could think that spinning a magnet about its axis wouldn't change its field would be if the angular momentum of the electrons was completely decoupled from the angular momentum of the ionic lattice making the bulk of the magnet. Thoughts?
     
  5. Sep 23, 2016 #4
    If you spin a magnet, the off-axis electrons in the magnet will generate a current. But this current will be canceled by all the off-axis protons in the magnet.
     
  6. Sep 23, 2016 #5
    If you spun something with some net charge, like the sphere on a van de Graaff generator, then you would perhaps generate some magnetic field.

    I think you were expecting some kind of coupling between the intrinsic angular momentum of the electrons and the orbital angular momentum of the electrons. The macroscopic rotation creates macroscopic orbits around the axis of rotation. This just generates plain current, which generates a magnetic field.
     
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