A Curie pendulum is a simple heat engine based on the lose of ferromagnetic properties of a material when it reaches the Curie temperature or Curie point.

We have a nickel (Ni) coin hanged from a copper wire so it is attracted to a magnet. A haet source is place below the coin and when it reaches the Curie temperature it is released from the magnet so it swings away from the magnet and cools down, so it gets ferromagnetic properties again and is attracted by the magnet again. And so on.

https://en.wikipedia.org/wiki/Heat_engine
https://en.wikipedia.org/wiki/Curie_temperature
https://en.wikipedia.org/wiki/Ferromagnetism
https://en.wikipedia.org/wiki/Nickel
https://en.wikipedia.org/wiki/Pierre_Curie
http://www.cienciabit.com