Science is a fun subject to learn – magnetism happens to be one of the more exciting topics one will ever have the pleasure of learning. Magnetism seems like magic at first glance, and it is certainly bewildering to see metal stick to surfaces for the first time, like in fridge magnets or toys. However, these magnets tend to weaken over time, as in fridge magnets falling off and magnetic toys not working like they used to. In truth, even those 'permanent magnets' are not truly permanent. This process is called demagnetisation, wherein a magnet's strength decreases or is eliminated naturally or artificially. Many factors can cause a magnet to weaken over time, as discussed below.
An overview of magnetism
Before going over how magnets weaken, it is important to first learn how magnetism works. As you may have already learned from your science tuition class, magnetism is a fundamental force in nature and occurs due to the motion of charged subatomic particles.
These negatively charged particles, called electrons, continuously rotate around their own axes and orbit around the nucleus. The former movement is referred to as electron spin and significantly contributes to generating repulsive and attractive forces referred to as magnetism. Essentially, these spinning and orbital movements are believed to create an electric current that results in individual electrons acting like small magnets (electromagnetism).
What causes weakened magnetism?
Unless their domains are accurately aligned, no magnetic material can be considered truly magnetic. Any changes in the direction of a domain could reduce net magnetic strength. Many different factors can cause these magnetic domains to change and randomise, such as:
1. Heat
Atoms constantly vibrate with varying intensity depending on their temperature or energy state, and any slight changes to this consequently affect overall magnetic strength. In short, a lowered temperature increases a magnet's strength, while a higher temperature causes the opposite effect.
As temperature rises, the atoms within magnetic materials vibrate much faster and in a more disorganised way, forcing some domains to become misaligned and reducing net magnetism. If the temperature increases further, all magnetic domains get pushed out of alignment, and the magnet completely loses its magnetism.
2. Improper storage
Proper storage ensures magnets retain their magnetism over time. Most magnets contain iron, which is known to rust when exposed to water and oxygen and changes the underlying chemical structure of what makes a material magnetic. Neodymium magnets, the strongest magnets in the world, are the most susceptible to corroding due to having large iron content.
Apart from improper storage, placing magnets close to other stronger magnets can also cause them to weaken. Identical poles of differing magnets should not be put close to or make contact with each as the stronger magnet will cause the magnetic domains of the weaker one to change direction.
3. Structural damage
Lastly, structural damage to a magnetic material or a reduction in its size will reduce its magnetism. As a refresher, a magnet's magnetic field depends on its size; the bigger the magnet, the greater the field it generates. As such, structural damage through chipping or other means reduces the magnet's size and, in turn, its magnetism.
Conclusion
Although many forces are conspiring to take your magnet's magnetism away, the net decrease in the long term is barely noticeable. As such, you can rest easy in knowing that the permanent magnets you use around the house will last long enough for your needs.
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