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We have an existing magnet (SmCo) that needs to be less powerful. Is there any way of doing this without altering its dimensions? I can imagine filing bits off it, adding spacers etc, but these are not options.

One suggestion is to partially demagnetize it. Is this even possible, given that degaussing is usually either all or nothing? Would a standard degausser even work on something with such a high coercivity? Is degaussing a progressive thing ie the longer in the alternating field the less magnetic it becomes?

Any other suggestions?

Dirk Bruere
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    Heating the magnet comes to mind (not melting, but 60-70 deg, for example). With warm/hot water. – a concerned citizen Nov 07 '22 at 12:16
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    Adding a small ferromagnetic path to "short" the magnetic field might be an option i.e. a tiny keeper from N to S. – Andy aka Nov 07 '22 at 12:23
  • @Andyaka No space – Dirk Bruere Nov 07 '22 at 13:45
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    @aconcernedcitizen The Curie point is way higher, and taking it beyond that point just kills it. Otherwise no effect – Dirk Bruere Nov 07 '22 at 13:46
  • I have no ferromagnetism knowledge, but would coating the magnets in some metal reduce its potency ? – Rahmany Nov 07 '22 at 13:53
  • @DirkBruere I never said to do it beyond the Curie point and the demagnetization doesn't happen abruptly. The higher the temperature the more chaotic the orientations (e.g. no longer aligned, all). Try it with a bowl of hot water (you'll need to leave the magnet inside for some 10-20 min). See how much it attracts before and after. Of course, the problem is keeping the temperature but, heating it is a solution. – a concerned citizen Nov 07 '22 at 14:37
  • @Rahmany, I'm just guessing that any coating that was thick enough to make a difference probably would alter the dimension of the magnet by more than the OP is willing to accept. – Solomon Slow Nov 07 '22 at 17:29
  • (Joking) Drop it or hit it with something. The harder or more often you hit it, the more demagnetized it gets. You could engineer a rig that would hit a magnet until it reached the desired strength. It wouldn't be practical, but it'd be funny as heck. – Wayne Conrad Nov 07 '22 at 21:28
  • @WayneConrad Or perhaps use ultrasonics to do that job? – Dirk Bruere Nov 07 '22 at 21:30
  • @DirkBruere If ultrasonics will do it, that'd be the pro way to do the silly thing – Wayne Conrad Nov 07 '22 at 21:38
  • On a more serious note: I'm sure you've thought of this, but do you have any freedom to modify whatever it is the magnet is too strong for? – Wayne Conrad Nov 07 '22 at 21:44
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    @WayneConrad None at all, except at large expense – Dirk Bruere Nov 07 '22 at 22:38

1 Answers1

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Yes demagnetizing is a partial thing.

The magnetic anisotropy is typically unidirectional for high coercivity magnets, meaning that the magnetic moments like to point into either of two directions on one axis.

When these magnets are sold, they are prepared such that almost the entire material has the moment aligned in the same direction. If you heat it beyond its Curie temperature and cool it back down, the orientation will be random (demagnetized). But anything in between are stable states, too, e.g. 50% of the material being aligned and 50% being randomly aligned. That way, the strength, i.e. external field will be reduced.

  1. Aligning it at room temperature is probably futile, but the higher you warm it, the lower its coercivity will become (reaching ~0 at the Curie temperature). So if you can heat and apply magnetic fields, just play a bit. If you accidently completely demagnetize it, it is rather easy to remagnetize even with small field as long as you apply them while cooling through the Curie temperature.

  2. Another way to reach partial magnetization would thus be to completely demagnetize it and cool it with a field which does not permeate the entire piece, leaving part of the material unaligned. But the field will not be uniform then.

  3. A third strategy, suggested by Andy in comments, is too coat the magnet with a soft-magnetic material, e.g. iron powder or iron foil. The coating will provide a low-reluctance path that some of the flux will take, reducing the amount of flux that goes into the "far field".

tobalt
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