So I’ve had this thought for 20+ years but can’t seem to get it to work. Maybe someone smarter than me can make it work.

The Curie point of Gadolinium is around room temperature. If you put a high powered magnet on one end and then generate some external heat and an include a spring (or crank arm) on the magnetic end, you could produce a piston, similar to a sterling engine.

Now, if you add this cooling material as a heat sink, you could likely rapidly cool the gadolinium material back below the Curie point, making a more efficient engine, perhaps even producing something that could do a bit of work.

I made some prototypes back in the day, but the ferromagnetic material would always eventually get locked with the magnets. My rudimentary engineering skills could never get the external heat source quite right. Perhaps someone with a bit more ingenuity will take this and run with it.

Also, old broken microwaves are a great way to salvage some pretty strong magnets.

And be careful when handling gadolinium, it’s known to cause kidney and nerve damage.