Nothing lasts forever, at least as far as we know. Just look at a pack of eggs, or your old shirts if you’re looking for proof of that idea.
On that note, while not the same detail, most objects will have a workable shelf life, before they are unceremoniously found to be useless, and thrown in the trash along with the rest of our junk.
This is a simple-to-understand concept and one that pretty much everything in our life follows. Food, clothes, appliances, and cars.
Heck, if you want to be a little morbid about it, even pets aren’t exactly going around living forever, are they?
But then we get to the objects that seem to buck this trend, or at the very least, we don’t think of as having a usable shelf life.
Things like a well-built home seem to stand forever, and a good road that is usable for generations to come.
However, there is one item most people often wonder about when it comes to shelf life, and that is the humble magnet.
How long do they last? Can they last longer than a hundred years? What causes them to lose their magnetic strength over that time?
And are there any ways to keep a magnet usable for longer?
All of these questions will be answered in this article!
How Long Do Magnets Last?
So, before we go any further into this topic, we should probably first answer the main question that we posed in the title of this article: How long do magnets last?
Well, the short answer is a long time. Like, a REALLY long time.
A magnet, with external factors affecting it, can last decades while still keeping its magnetic qualities.
Magnets can keep their magnetic properties for over a hundred years, and still only lose around 1% of their magnetic field strength.
And even here, this isn’t the magnet losing all of its pulling power this time, only when its field begins to weaken
Now, that is a long time and perhaps shouldn’t come as too much of a surprise to people who know the materials and metals that most magnets are made from.
Magnetic Creep
However, despite most magnets ostensibly having incredibly long shelf lives, many of us have observed, whether it was over decades, years, or even months sometimes, that a magnet can visibly lose its strength.
So, what exactly is this about? What goes into a magnet losing its… well, magnetism?
Well, as we know, a magnet’s properties are the result of the magnetic field that the object generates, as the atoms of the object align in such a way that combined, creates a strong enough magnetic field to affect other objects with a similarly stronger-than-average field.
Demagnetizing
However, a magnetic field is not a permanent force that will exist forever.
Newton’s second law of thermodynamics states that energy in places of high concentration will move to areas with less energy, causing entropy to increase.
And, while magnetic fields were not nearly as well-understood centuries ago, the same principle still applies. Magnetic fields will also lose that energy over time.
This phenomenon, where demagnetizing forces slowly but surely weaken a magnetic field over time, is usually referred to as ‘magnetic creep’.
Mainly because, when treated properly, it takes a long time for the magnetic field of a given magnet to noticeably weaken. It creeps up on you, so to speak.
However, these are primarily in ideal conditions, and many magnetic objects are often not kept in places where their properties are best protected.
Factors That Can Decay Magnet Strength
So, what sort of factors can affect a magnet’s strength over a long enough period?
Volume Loss
One of the major factors that can cause a magnet to slowly lose its magnetism over time is a loss of volume.
If a magnet is kept in conditions where it can be subjected to rust, or other forms of corrosion, the metal that the magnet is made from can break down into other molecules and materials, such as iron to iron oxide, for example.
This leaves a magnet with less mass to maintain its field, causing it to weaken faster than it otherwise would.
Alternatively, on a much more simple note, a magnet can still be chipped or broken over time, at least when put through enough stress or hard enough force.
These chips similarly break off and lower the mass of a magnet after a while, further contributing to the weakening of the field.
This is why, when storing magnets, you should be keeping them in a location where they are secured, and away from conditions where corrosion will occur.
It’s not just to keep the magnet looking pristine and new, but to help it keep working over longer periods!
Demagnetizing Elements
As we have already mentioned and implied, demagnetizing forces are almost always at play on a magnet, whether they are kept securely or not.
However, these forces are usually incredibly weak in normal circumstances, which is why magnets do last a long time.
But a magnetic field can sometimes be affected by other magnetic fields that cause it is own to weaken, especially when they encounter much stronger magnets.
This can be the case when magnetic alloys are exposed to much stronger magnets, such as in the case of ceramic strontium ferrite, for example.
Keeping your magnet away from other magnetic fields is the best solution to this problem.
Heat
High temperatures are an especially effective way for magnets to lose their properties, as the excess heat energy disrupts the structure of the atoms in a magnet, causing the field to act strangely and weaken.
While many magnets will return to normal if not taken to a critical point, it is best to keep magnets away from strong heat sources.
Final Thoughts
So, there you have it.
While magnets can last a very long time in the right circumstances, many factors can weaken them over a long enough time.
Make sure to keep your magnets safely stored and secured!
