General Question

El_Cadejo's avatar

I just held a lighter to a magnet and it lost its magnetism. Why?

Asked by El_Cadejo (34547points) December 14th, 2008

I know it has something to do with the poles shifting, but can someone explain it more in depth and why this happens?

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7 Answers

artificialard's avatar

This is too science-y for me but there’s a well-documented experiment here concluding the fact that heat reduces magnetic fields (or force, or whatever).

waterskier2007's avatar

i believe magnetization has to do with the alignment of the magnetic dipoles in the material, so it could be possible that due to increased heat, the magnetic dipoles were disaligned due to easier movement. i know that in general heat allows better movement of molecules, defects, etc. so it could apply to the magnetic dipoles.

i could be completely wrong though

hannahsugs's avatar

Without looking anything up, I believe that waterskier has the right idea. The basic idea is that every molecule in the metal has its own, small magnetic field. If the molecules are all scrambled in different directions, there is no “net” magnetic field, because they cancel each other out. If the molecules all point in the same direction, the magnetic field has an additive effect, making a magnet!

“Heat” is essentially a measurement of how much motion the molecules of a material have. The more motion, the more heat. By heating up a magnet, you are forcing the molecules to move around faster, and when they finally “settle down” again (they are still moving, but not as much), there’s no reason why they would all line up in the same direction. Hence, no more magnet.

it’s finals week and i’m not getting much sleep. sorry if this is incoherent

Harp's avatar

Magnetism varies according to the crystal structure of the metals composing the magnet. These crystals have different configurations depending on the metal’s temperature and cooling conditions. Ferromagnetic materials, those used in most permanent magnets, have a certain temperature, known as the curie point, at which the crystal structure transforms to a different phase. This new crystal phase is non-magnetic.

In carbon steel, this temperature is 1333F. At this temperature, the crystal phase known as Austenite forms. Austenite is completely non-magnetic. As the steel cools, other crystal phases will form that are susceptible to magnetization, but the steel’s magnetic alignment from before heating will have been lost, and the steel will have to be re-magnetized.

Knotmyday's avatar

What about non-ferrous magnets? Good stuff, @Harp.

Harp's avatar

“Ferromagnetic” materials aren’t necessarily ferrous, despite the nomenclature. For instance, cobalt and nickel are ferromagnetic, as are other alloys that don’t contain iron. All these will have a specific curie point.

waterskier2007's avatar

harp is probably right, but ferromagnetic just means that it keeps magnetization after it is removed from the external magnetic field. the other two are diamagnetic and paramagnetic materials and the difference between the two is whether the induced magnetic field is in the same or opposite direction of the external field. these two lose magnetization after they are removed from the field

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