If I take two ceramic permanent magnets and hold them in firm contact North to North, or South to South, will they eventually become weaker?
If so, what would be the timeframe and are there any other types of magnets that would be less susceptible to weakening?
I have heard conflicting opinions on this. Can anyone clear it up for me?
Thank you,
John Medlow
Not eventually, right away. If you could accurately measure the flux at the surface of those magnets before and after such an experiment, you would see a small reduction in magnitude. However, once the experiment has been done, the reduction after subsequent similar experiments gets smaller and smaller. The magnet gets more stable after it has had its strength knocked down a bit. The least stable domains get flipped first.
Rare earth (samarium cobalt and neodymium iron) are some of the most resistant to being demagnetized this way. Pairs of them make good compression springs.
Now you have another opinion to add to your collection.
And AlNiCo magnets have little enough coercive force that you have to place a "keeper" across the poles, or just the magnetomotive force required to push the flux lines across empty space will demagnetize them significantly (and immediately).
If you've heard differing opinions it's probably because there are different kinds of magnets out there, with different behaviors in this regard.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
Weaker ... yeah somewhat, but they are generally rugged compared to their ferrite cousins . Timeframe ... depends on how long you keep them together but If you place them near a Neodymium Iron Boron they will weaken bloody fast. The Nd Fe B are the toughest and best permanent magnets .
theJackal
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