Found this from Gerald O'Docharty in the message base, never realized
there was such a drastic difference. The curie point is a temperature
where magnets lose their magnetic field entirely, though when they cool
down, the magnetism is restored. My understanding is for normal ferrite
magnets, the curie point is about 180 degreed F. So I was surprised to
see this comment;
The fact of the matter is however that the curie point for most ND
magnets IS 300 degrees C. I have several data books from Big time magnet
manufacturers that specify this explicitly, as well as having followed
the trade journals for years. This is the main disadvantage as a matter
of fact with the Neodymium -Iron -Boron magnets when used in
applications such as motors where there is the chance of a high
temperature rise. Although they have the strongest MGOe rating of any
industrial magnetic material and are used in some servo motors, special
care has to be taken to insure they dont get too hot, or they will
suffer irreversible demagnetisation. this is why most motors that
specify rare earth magnets are using Samarium Cobalt. Its curie
temperature is typically 680-700 degrees C.
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I have heard that if you freeze a magnet the field intensity will
increase, but I don't know if it stays that way once brought back to
room temperature. Just thinking along the lines of other ways to bring
a magnetic field in and out....
-- Jerry W. Decker / jdecker@keelynet.com http://keelynet.com / "From an Art to a Science" Voice : (214) 324-8741 / FAX : (214) 324-3501 KeelyNet - PO BOX 870716 - Mesquite - Republic of Texas - 75187