Other than being magnetic, that is. If you had two identical iron bars and magnetized one of them, how else would it differ from the regular one? Would electricity flow the same? Would it transfer heat the same? Have the same bending/breaking strength? etc. Is there anything different about a magnetic piece of metal other than it being a magnet?
IANAPhysicist, but as far as I know, nothing. In ferrous metals, the atoms are simply lined up so that the zillions of electrons create a macro/net-effect of a poled charge across the material.
Perhaps this might make a ferrous bar of iron more brittle than a non-ferrous one, but that I don’t know.
the behavior of some of the electrons is what makes the magnetism.
the iron has to have a quality to be magnetic. if you had two samples of the quality to become magnetic and then magnetized one (causes some of the electrons to have their spins lined up ) the difference would be the spin of some electrons and this creates magnetism but no other change.
:smack: I’m using ferrous wrong in this context.
I meant magnetic vs. non-magnetic piece if iron (or nickel or whatever).
AIUI, magnetizability (and brittle transition temperature) in ferrous alloys result from a body-centered-cubic (BCC) crystal structure, but not face-centered-cubic structures.
Don’t ask me why.
I just realized that the original subject is a bit confusing. I’m not asking what differences various metals have that make some metals magnetic and others not. I’m asking if there would be differences between two pieces of the same metal which are exactly the same except one is magnetized and the other is not.
So when the spins are lined up, does not that not change the electrical resistance? Or the electric field lines?
First off, the word you want is not “magnetic”, but “magnetized”. A minor detail, but it might make it easier to find more information.
And this is far from my specialty, but I would expect differences in structural strength between a fully-magnetized and unmagnetized piece of iron, with the fully-magnetized piece being both harder and more brittle (in other words, the magnetization would act to temper the iron).
I would not, however, expect the differences to be all that significant, especially since it’s extremely difficult to completely magnetize a significant-sized chunk of iron. There are always small domains of magnetization aligned in various ways, and magnetizing a chunk as a whole generally means increasing the size of some domains and decreasing others, but it’s really hard to get rid of the wrong-direction domains entirely.
Nit: tempering reduces hardness and brittleness.
I might have my terminology mixed up. What do you call the process where you heat up a piece of metal and then suddenly quench it?
The general term is strengthening.
quenching
We’ve always called that “hardening,” with lots of subcategories based on the details of the process. It increases hardness, but unfortunately also brittleness. Tempering involves less heating and slower cooling, and gives up a bit of the new hardness, but increases toughness and decreases brittleness.
No ! Magnetization is in no way a metallurgic technique for improving strength/toughness/hardness down at the steel foundry! Magnetization in fact changes no other property, it doesn’t influence conductivity… The Ferro-magnetism is stored in an inner electron, but only if the crystal structure and hence internal structure of the iron atom, is correct.
Austinite , face centre cubic, is not ferro-magnetic… there is no suitably constrained unpaired inner electron… BTW Most but not all stainless steel is austinite…
Only tempered steel remains strongly magnetized, so that’s why a permanent magnet is brittle.
You can of course magnetize your un-tempered nail, but its temporary .
In fact there are two types of magnetization … All atoms can be magnetized in the effect called parra-magnetism. which results in the atoms pushing away from the field… The idea is that the bring a magnet up to your finger, and your finger is repelling from the magnetic, N or S… But its VERY VERY tiny force , hard to demonstrate and completely forgettable.
So the specific thing about the iron atom is that in some inner shell arrangement (as iron is multi-valent… ) of iron, there is a single electron in an inner shell that is constrained (constrained from acting paramagnetically … electron pairs behave paramagnetically, outer electrons are free to change their orbits and thus are paramagnetic… but the special unpaired inner shell electrons may be ferro-magnetic ! )
And it turns out in iron/steel, that the change in orbit is permanent , unless its pushed back. (Hysteresis drives its crazy … Oh I am sorry, I know there’s no womb for such comedy here… Look up hysteresis. )
The ferro-magnetic inner shell electrons also appear in some rare earth metals, the ones with names I cannot pronounce nor spell, and it turns out that they do a better job of it… a stronger permanent magnet.
I would guess that the magnetized piece of metal is under a little bit of strain from it’s own magnetism that has to be opposed by the tensile strength of the metal.
Isilder, I thought paramagnetism was a weak attraction and it was diamagnetism that’s a weak repulsion. Which did you mean?
Wouldn’t magnetization decrease its energy, thus making it very slightly lighter?
If you take two strong magnets and stick them together, it takes considerable force to pull them apart. Would that same principle affect the tensile strength of a single piece of magnetized metal? As a magnetized bar of metal was being stretched, would the magnetic force within the bar resist the stretching and require more force to break it?
My gut says, “no to nominal” since the bar would stretch from its center and the magnetic force is canceled out between the poles; taking the path of least resistance too.
But there may be something to that.
ETA: Also, once you begin stretching the material, I wonder about the atomic structure to maintain its magnetic alignment. Will a ferrous material begin to demagnitize in some fashion if you begin to stretch it?
In the sense of something actually done in practical applications, certainly not. As I said, I would expect it to be a very small difference, and very difficult to achieve. But that doesn’t mean that there would be no effect at all. My thinking is that it would work by enforcing uniformity of crystalline structure, and that growing a single magnetic domain to encompass the entire object might drive out defects.
And you’re a bit mixed up about paramagnetism. All materials are diamagnetic, which causes repulsion from a magnet. Some (but not all) materials are paramagnetic, which causes attraction to a magnet, and when paramagnetism occurs, it’s stronger than and overwhelms diamagnetism. A few materials are ferromagnetic, which also causes attraction to a magnet, but which is different from diamagnetism in that the material can remain magnetized even after the external field is removed (this is called hysteresis). Ferromagnetism is also usually stronger than paramagnetism.
Aside from superconductors, which are a whole other story, there is one material that’s diamagnetic enough that thin films of it can be levitated by a magnet- Pyrolytic carbon. See Diamagnetism - Wikipedia
Nineteen posts and not a single Insane Clown Posse reference. 