Super-Cooled Flint

[InspectorTaylor]

I was wondering if anyone could tell me why flint becomes magnetic when you freeze it with liquid nitrogen? I was playing around the other night freezing whatever material I could find laying around just for fun when the piece of flint was sucked right out of the dish and stuck to the magnet I had. I was pretty sure it wasn't naturally magnetic but just to make sure I grabbed another piece I had and checked. The magnet had no effect on that piece, but the frozen one sure was magnetic. It slowly lost its attraction to the magnet as it warmed back up and was back to being non-magnetic somewhere close to 0 degrees C. I repeated everything several more times just to make sure I wasn't crazy. So what's going on? I know superconductors will make a magnet float above it, but I haven't ever heard or read about making material magnetic by freezing it. Are there any similarities between these two phenomena?

 

[asimpson]

Some components within the flint have Curie temperature between room temperature and -200 deg C. Not sure which. Below these temperatures material becomes Ferromagnetic and strongly attracted to magnet.

 

[hacksaw]

most flint is ferromagnetic at room temperature or marginally so depending on the grade and temperature

 

[EdStainless]

There are metals that do this also, simply depends on the curie temp.

This effect has industrial uses and some alloys exist with tightly controlled curie temps.

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Plymouth Tube

 

[hacksaw]

believe the material referred by the OP is classified as an intermetallic