Magnets are objects with magnetic moments. Some substances, such as iron, cobalt, nickel, etc. There is a magnetic moment in the molecule. When the molecules of such substances are arranged neatly in the direction of magnetic moment, their whole bodies will present magnetic moment and become magnets. Disrupting the molecular arrangement inside the magnet will make the magnet lose its magnetism.
Heating can strengthen the thermal motion of magnet molecules, and when the temperature (molecular motion) reaches a certain level, the magnet will lose its magnetism. At this time, the magnets can be easily separated. When the temperature does not reach to change the internal structure of the magnet, the magnet will recover its magnetism when the temperature drops. The magnetic switch that disconnects the control circuit when cooking in the old rice cooker works by this principle.
Magnets made of different materials have different degaussing and permanent degaussing temperatures.