Magnet Freezing

When You Freeze A Magnet, Does it Regain Some Of Its Power, or does it stay the same, Or Lose power? just a simple question ive been wondering

I don't think anything would happen. You are not changing its state of matter - so the molecules are still going to be in the same pattern as before it was put into super-cool temperatures.

A better question would be, what would happen if you melted it, and then let it "freeze" (become solid) again?

I bet that the magnet would lose a lot of its strength, maybe all of it, as the magnetic alignment would be thrown way off for all the molecules within it.

But then again, if there was a strong magnetic field in the area where the liquid metal was, and you could prevent the liquid metal from splattering out and towards the magnet, then when it "freezes" it should be very strong - as all the molecules would be correctly aligned.

Thanks Yarium. Thats An Interesting thing to try... hehe.

We also performed several freezing tests to see if freezing a magnet would change its chemistry and therefore its strength. We found that by freezing a magnet its weak crystal lattices would straighten into correct formation from the shock and actually increase the magnets strength in the range of 0.02% to 0.16%.

www-ed.fnal.gov...

-DT

Originally posted by Yarium
I don't think anything would happen. You are not changing its state of matter - so the molecules are still going to be in the same pattern as before it was put into super-cool temperatures.

A better question would be, what would happen if you melted it, and then let it "freeze" (become solid) again?

You seem to be assuming that all magnets are solids and that any change in temperature of the body will have no effect on the chemical makeup of the material. This is incorrect, there are liquid magnets, but this is not to say they exhibit the same strength as do solids, because they do not.

And freezing a body inhibits the movement of molecules, the intermolecular forces. I do not know much about magnetism, but when the movements of the molecules exhibit neglible vibration, translation or rotation, they can become superconductive. I am offering this as an example of another physical phenomena which takes place at such conditions. So I will say it may very well have an effect on the magnetic strength, but it could very well be neglible and not a real concern.

I think though, a simple google search could have fufilled this thread.

Originally posted by Frosty
You seem to be assuming that all magnets are solids and that any change in temperature of the body will have no effect on the chemical makeup of the material. This is incorrect, there are liquid magnets, but this is not to say they exhibit the same strength as do solids, because they do not.

Well, to a large degree, the temperature of a body does not affect its chemical make up unless the energies are high enough or low enough to make a change in the state of matter. A lower temperature means a low average energy level per molecule, which means less "jiggle" so to speak (less movement).

Superconductors work at extremely low temperatures because, at that level, there is less "other energy" (aka, resistance) that's getting in the way of the shifting electrons (usually in the form of heat). I will also point out here that Plasmas are also super-conductors, because instead of restricting electrons, plasmas create electron clouds since they're so energetic that the nuclei of the atoms are freed of any electrons - and so electrons can pass through with amazing ease.

Now, what makes a magnet strong is that most of the molecules in its structure are correctly aligned to the magnetic field of the others molecules in the structure - strengthening the overall magnetic field AAD (At A Distance... a term I'm going to use from now on because it comes up so much in physics).

What makes a magnet weak is that some of the molecules in the structure as misaligned - their polarities are not in sync with the others. This cancels out a similar amount of strength in the magnet. The more misaligned molecules are present, the weaker the magnet.

So, a liquid magnet is very likely to be a weak magnet - because its molecules have so much freedom, that they'll rarely all be aligned correctly to make any significant magnetic fields AAD.

However, a liquid magnet, by having such free-moving molecules, would be able to easily be aligned correctly and easily by the presence of a strong magnetic field. The liquid magnet would then "snap" into place. However, being a liquid, it would not form the nice, traditional "bar" magnet that we're thinking of.

Remember those iron sillings back from Grade 9/10 science? And how you could spread them out on a table-spot and use them to "see" a magnetic field? This is exactly how the liquid magnet should respond (I use should here because I've never heard of this being done). Notice, though, that much of it will try to jump to the magnets themselves. Chances are that you don't want this happening to liquid metal, due to the amazing heat involves.

You are looking for the phenomenon known as "Curie temperature".

Ferromagnets go through a phase transition when heated beyond a certain temperature, depending on the details of the substance, upon which they lose their
magnetization.

The interaction between magnetization, atomic physics and temperature has a long history in physics. It is sufficient to say that we know a whole bunch about it.

thanks for the responses

All magnets have something known as the 'Curie temperature', as some posters already mentioned. If you heat a magnet hotter than this temperature, it changes from a ferromagnetic material (like iron, nickel cobalt are when colder than their Curie temps) to a paramagnetic material (like aluminum or titanium). When you cool the magnet back down again, it will recover it's properties and become ferromagnetic again, as it was before.

By Yarium: Now, what makes a magnet strong is that most of the molecules in its structure are correctly aligned to the magnetic field of the others molecules in the structure

This is a good description of ferromagnetism

By Yarium: What makes a magnet weak is that some of the molecules in the structure as misaligned - their polarities are not in sync with the others. This cancels out a similar amount of strength in the magnet. The more misaligned molecules are present, the weaker the magnet.

This is a good description of paramagnetism

Here's something I am wondering, though. Is the Curie temperature for a metal always lower, always higher, or sometimes higher/sometimes lower than it's melting point? I ask this because it pertains to Yarium's points about liquid magnets, and how valid those points are or not.

A good book I used for a materials engineering course I took last term is "The Science and Engineering of Materials" 5th ed, by Donald Askeland/Pradeep Phule. It talks about, among many other things, the magnetic nature of materials. (unfortunately, it is also probably the book with the most typos ever, including in some of the math, but if you can get past those, it's factual information is great!)

Originally posted by Yarium


Superconductors work at extremely low temperatures

Not true. The highest record temperature for a working superconductor is about 140k.

Originally posted by DragonsDemesne
All magnets have something known as the 'Curie temperature'

No, ferromagnets have a Curie temperature. Antiferromagnets have what is called a Neel temperature and Ferrimagnest exhibit a Curie transition temperature, above this temperature the substance is paramagnetic and below it is ferromagnetic.

This is what I could find out about Curie temperatures and boiling points, but I do not know much about this, if anything. I don't know what any of these means or applies to (not quite my level), but maybe it could help you:

Curie temperature:
Theta=Npu²a/3kW

Theta, I believe, comes from the Weiss equation if I am reading correctly, I only say this because the Weiss equation is listed above the above equation in my book.

[edit on 26-1-2006 by Frosty]

Originally posted by Frosty
Not true. The highest record temperature for a working superconductor is about 140k.

Not to be arguementative Frosty, but this is because they're doing research into raising the temperatures of superconductors so that they don't require super-cooling units, and so can become something much more widely used.

So it's not like those "high temperature" super-conductors exist naturally.

Originally posted by Yarium


So it's not like those "high temperature" super-conductors exist naturally.

And I suppose liquid helium is frequently encountered in nature?

Gack, whoops, my mistake, yes only ferromagnets have a Curie temperature.

From "The Science and Engineering of Materials" 5th ed, Askeland/Phule (2005) the superconductor with the highest critical temperature is Hg0.8Tl0.2Ba2Ca2Cu3O8.33 with a critical temperature of 138 K at ambient pressure.