In out article Why are only some substances magnetic? we looked at what goes into making something magnetic. This of course leads on to the question “Can something that is magnetic ever wear Out?”. Certainly toy magnets sometimes come with warnings not to drop them or heat them up, lest they lose their magnetic power.
So, if you have ever used a a toy magnet you may have noticed that even if they are treated with care, magnets eventually, albeit very slowly, lose their strength.
This is because magnets owe their properties to the existence of vast numbers of “domains”, each around 1mm across, packed with atoms whose spinning electrons are aligned. This highly ordered state is the origin of the magnetism and also of the vulnerability of magnets to heating or dropping, which jolts some of the domains out of alignment.
Even if a magnet avoids such a fate, it will eventually fall prey to the effects of ambient heat and electomagnetic fields, which damage the aligmnent and steadily weaken the magnetic force. Fortunately, it is a very slow process; a modern samarium-cobalt magnet takes around 700 years to lose half its strength.