MadSci Network: Physics

Re: What type of magnets would be best to use in thermal experiments?

Date: Mon Jan 31 08:00:45 2000
Posted By: Eder Molina, Researcher PhD, Dept. of Geophysics, Institute of Astronomy and Geophysics - USP
Area of science: Physics
ID: 948837281.Ph

In my classical experiments about the effect of temperature
on magnets, we did not use magnets, because they are expensive
and, after demagnetized, cannot get the fully magnetization
again. So, we magnetised a steel blade, by using a strong
magnet and pressing it against the blade, sliding in the
same direction many times, until the material was magnetised,
what we could see by attracting little metallic objects with
it. Then, we began to heat this "home-made" or "school-made"
magnet, and noticed that, as we increased the temperature,
the material became non-magnetic at a certain temperature.

In practice, we use a metodology similar to this to investigate
the "fossil magnetic field" recorded in some rocky material
(basalt, in most cases). If we are under normal temperature,
the magnetic domains are strong enough to mantain the preferential
direction of magnetization, and the rock behaves as a magnet.
If we heat the material, the thermal effects conterparts the
magnetic intrinsic force in the material, until at the Curie
temperature (about 600-800 Celsius for most magnetic
minerals), the heat destroys the magnetic domains, and the
material behaves as a non-magnetic mineral. Of course, this
kind of experimentation is done with very sensible equipment
and techniques, but I've described it just to illustrate an
application of this experiment in the real world.

I think you could try to using some metallic (iron made) material
to magnetized and them demagnetize them. If you do so, you are
showing interesting effects about magnets (that some materials
can obtain magnetization when exposed to strong magnetic fields,
that the temperature conterparts this effect, and can even
remove the magnetization of a magnet).

Best regards

Eder C. Molina
Dept. of Geophysics
Institute of Astronomy and Geophysics
University of Sao Paulo

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