Little Question about magnetization and heat

[rauven]

Hello, I'm new so i hope I'm not posting this question on the wrong section, anyway, here's the question:

Is possible to magnetize metals with heat?

I'm asking because today i found out that my scissors became slightly magnetic after being in touch with fire for a while (i was using them as tweezers).

I don't remember having them near any magnets so that's why I'm curious...

thanks

 

[Crazymechanic]

Hi and welcome to PF.

Well commercial magnets are made usually heating the metal or alloy and then exerting external magnetic field while it cools so that the atoms and electrons align to create this kind of phenomenon as we call magnetism. There are other ways too like wrapping a wire around a metal and connecting the ends of the wire to a direct current source.Although this usually doesn't end up as magnetizing the metal for a long time and depends on the voltage/current used and other factors.

Magnets can demagnetize if exposed to heat because of the rupture of particle alignment in the material that was responsible for the magnetism in the first place.But to answer your question I haven't heard nor seen in my own experience that a metal being heated by any means with no external magnetic field would become magnetic. Only the other way around that metal while exposed to heat can loose it's magnetic abilities.

Maybe you had a coincidence that while your scissors were cooling down they experienced somekind of a magnetic field , and it doesn't always have to be a permanent magnet like the one from a fridge sticker or speaker as you would think it could be some electrical wires or equipment.
Although most electrical wiring in house uses the mains AC which can't induce long term magnetism because the polarity is constantly changing.

 

[Khashishi]

Ferromagnetic materials like iron always have magnetic domains. Each domain is like a little bar magnet. But, in an unmagnetized piece, the domains are small and jumbled so their magnetizations cancel out. If you heat up a piece, it becomes easier for the domains to flip and meld, so when you cool it down again, the domains might not cancel out anymore, and it becomes magnetic. But if you do this in an uncontrolled manner, you could just end up demagnetizing the piece again.

If you expose the piece to a magnetic field when it is hot and slowly cool it off, then it should become magnetic.