Why does higher temperature and mechanical stress have a negative effect on the magnet's strength? Think of a collection of atoms as representing the magnets. They all have arrows on them pointing different ways, because each atom is a little magnet that works to create a bigger one. In a more perfect magnet, all the arrows are pointing the same way. In a not-magnet, the arrows are pointing all different ways. When a ferromagnet (permanent magnet such as on your refrigerator), the arrows jumble up and point different ways. Because heat is actually the microscopic shaking of atoms and molecules, it has the same effect as the macroscopic shaking of dropping the ferromagnet. Oh look, a picture.