How do heat and cold affect magnetism?

Magnetism is affected by temperature in different ways. Magnetism relies on the alignment of atoms, with each atom having its magnetic spin in the same direction. This is more pronounced in a solid material, since the atoms are locked in a rigid structure and their spin is controlled by that structure. Heating the material will allow the atoms more thermal energy, increasing their movement; the more they move, the less they are lined up and so the magnetic forces become weaker. At a specific point, called the Curie Temperature, the material's atoms will become so dissociated that the magnetic forces vanish entirely; since the atoms can no longer align themselves, they can't put out enough of a magnetic force to be noticeable. Conversely, low temperatures (cold) can increase the power of a magnet, since low temperature means that there is less energy in the atoms, and they are more solidly locked into their position in the material.