Re: Do Permanent Magnets Dissipate?

Juno wrote: 
Hello all,

The subject title pretty much describes my question. I was discussing
various topics, such as electricity, theory, and forces of friction and
magnetism with a friend of mine when he asked me if permanent magnets
slowly lose their magnetism over time. I honestly didn't know the
answer, and searching Google didn't help me either. I know that
traditionally, there are only four ways to demagnitize a magnet:

    * Heat. Heating a magnet past its Curie point will destroy the long
range ordering.
    * Contact. Stroking one magnet with another in random fashion will
demagnetize the magnet being stroked, in some cases; some materials
have a very high coercive field and cannot be demagnetized with other
permanent magnets.
    * Hammering or jarring. Such activity will destroy the long range
ordering within the magnet.
    * Being placed in a solenoid which has an alternating current being
passed through it. The alternating current will disrupt the long range
ordering, in much the same way that direct current can cause ordering.

(Found at Wikipedia:
http://en.wikipedia.org/wiki/Permanent_magnet#How_to_demagnetize_materials)

However, I don't know if permanent magnets will simply lose their
forces of magnetism over time. Personally, I don't see why they would,
as I can't see any force(outside of the four listed) that would work on
them to lose their magnetic abilites. Does anyone know the answer?
Thanks in advance for any help.

Cheers,
Juno

temperature is a statical sort of thing. Even at temperature well below the curie temperature, there is a non zero chance that a given domain will momentarily get hit with an effective thermal energy that approaches what it would see at the curie temperature. So there is not a perfect magnetic stability, even below the curie temperature. For some materials, like hard steel, magnetism decays with a half life short enough for the effect to be directly observable. With high coercivity materials, samarium cobalt or neodymium, the decay rate is very much slower. I think the term that describes this effect is magnetic disaccomodation.

There is an analogous effect for dielectrics that have been polarized with an electric field (electrets and piezo transducers).
.

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