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Q & A: Curie temperatures

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Most recent answer: 10/22/2007
Q:
I want to know how can I show to my teacher that iron have different magnetic ability in different temperature?
on the other hand I need an experiment sketch.
I want to show that in temperature higher than 769 C iron isnít magnetic any more
- MM AA (age 20)
A:
That's realtively easy to do if you have access to a temperature controlled oven, especially one with some electrical leads going into it.  Without knowing what sort of school you're in, it's very hard to guess what sort of equipment is available. Let's say that somehow you have access to an oven that goes to 769įC (the Curie temperature of iron) and has a window you can see through, but no wires. Maybe you could suspend two iron magnets by copper wires, with the magnets pulling on the wires due to the magnetic force between them. (You have to be very careful here not to use any materials that would melt, vaporize, or burn.) When the temperature reaches 769įC, the force between the magnets will fall to nearly zero, and the magnets will hang straight down. Actually, that should happen at somewhat lower temperature, because although the iron will still have magnetic domains, the domains will start realigning and  losing net magnetization before they individually cease to be magnetic.

When you let the iron cool back down, the magnetic domains will re-form, but without any overall net magnetization, so there still will be very little force between the pieces of iron.

If you donít have access to the right sort of oven, you could look for some other magnetic alloy with a lower Curie temperature to illustrate the same point.

Mike W.

Lee H
Mike.  This seems like an experiment I would
not recommend. 769C is bloody hot.  Without proper equipment
and proper supervision it is potentially dangerous.
I would add the Letterman warning:  "Kids, don't try this
at home".

(published on 10/22/2007)

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