Show Me Some Science! Ferromagnetic Failure
Canadian coins are made primarily of steel, which is a ferromagnetic metal. This means these coins will become magnetized when placed near a strong permanent magnet, and attract the magnet. Unpaired spinning electrons act as tiny magnets, and many of these will line up to the magnetic field of the strong magnet.
However, above a certain temperature, called the Curie temperature, ferromagnetism suddenly disappears. Random thermal motion disrupts the long-range alignment of the electron spins, and the coin no longer is attracted to the magnet. Once cooled down again, the ferromagnetism returns.