Do Magnets Lose Strength Over Time? What Science Says

From wine and cheese to leather boots, many things in life are known to get better with age. Sadly, magnets aren’t one of them. If you’ve ever had fridge magnets that once held papers securely but now slip down with ease, you’ve already witnessed the slow fading of magnetic power.

Despite some magnets being labelled as “permanent magnets”, it’s important to note that no magnet is truly permanent. Like many things in nature, magnets can lose their strength over time, a process called demagnetisation. This usually requires external interference, such as heating or striking the magnet, but natural wear and tear also play a role. Let’s take a closer look at how magnetism works, why magnets weaken, and what can be done to restore their powers.

How does magnetism work?

Before we understand how magnets weaken, it helps to know what makes them magnetic in the first place.

Magnetism is one of the four fundamental forces of nature, alongside gravity, the weak nuclear force, and the strong nuclear force. It originates from the behaviour of electrons – those tiny, negatively charged particles orbiting the nuclei of atoms. Electrons don’t just orbit; they also spin around their own axes. This spin is intrinsic and contributes greatly to the magnetic effect.

You can think of electrons as miniature magnets. Their movements produce magnetic dipoles or tiny magnetic fields, which combine to create a net atomic magnetic dipole moment. While protons and neutrons also contribute slightly to magnetism, their impact is negligible compared with electrons.

Why isn’t everything magnetic?

If every electron behaves like a tiny magnet, why isn’t your teacup, book, or biscuit tin magnetic? The answer lies in a fundamental principle of quantum mechanics: Pauli’s Exclusion Principle.

Electrons often pair up with opposite spins in the same orbital shell. When they do, their magnetic effects cancel each other out. In most materials, these cancellations mean the overall magnetic effect is zero.

However, a surprising fact about certain metals and elements like iron, cobalt, and nickel is that not all of their electrons pair up. These unpaired electrons contribute strongly to magnetism, making these elements ferromagnetic. In ferromagnetic materials, atoms group together in regions called magnetic domains. Within each domain, electrons’ magnetic moments align in the same direction, creating a net magnetic field.

When all the domains in a material align, typically after exposure to a strong external magnetic field, the material becomes a permanent magnet. That’s how your fridge magnets and powerful industrial magnets get their strength.

This concept often fascinates students in a science workshop in Singapore, where magnetism experiments demonstrate how aligned domains make all the difference between a magnetic and non-magnetic material.

The reason magnets lose strength over time

A magnet’s strength depends on its domains staying aligned. Unfortunately, a variety of factors can nudge these domains out of position. When enough domains fall out of alignment, the magnet’s net strength decreases. Here are the main culprits:

1. Heat

At the atomic level, particles are constantly vibrating. The higher the temperature, the more intense these vibrations become. When a magnet is exposed to heat, its atoms vibrate so vigorously that some domains shift out of alignment.

At a critical temperature known as the Curie point, the material loses all magnetic properties because the domains can no longer stay aligned. For example, neodymium magnets lose magnetism at around 310°C, while alnico magnets withstand up to 860°C.

Everyday life rarely exposes magnets to such extreme temperatures, but even moderate heat can weaken them gradually. Interestingly, cooling a magnet can temporarily boost its strength, while reheating it below the Curie point allows partial recovery. Once the Curie point is exceeded, however, permanent damage is done.

2. Improper storage

It may seem trivial, but how you store magnets matters. Magnets often contain iron, which is prone to corrosion when exposed to moisture and oxygen. Neodymium magnets, among the strongest available, contain over 60% iron and are particularly vulnerable. Rust disrupts the chemical structure responsible for magnetism, reducing strength over time.

Proximity to other magnets also plays a role. Placing a weaker magnet near a stronger one, especially with like poles facing each other, can alter the weaker magnet’s domains. In some cases, its poles can even flip, a process known as hysteresis loss.

This is why schools and secondary science tuition classes often advise proper storage practices for magnets used in experiments. It ensures consistent results and keeps magnets useful for longer.

3. Physical damage

Magnets are not immune to the wear and tear of daily life. A chipped or cracked magnet is smaller and, therefore, generates a weaker magnetic field. Sharp impacts, like dropping or hammering a magnet, can also jostle domains out of alignment.

The effect depends on the magnet’s material. Neodymium and ferrite magnets are brittle and prone to shattering, while alnico magnets are tougher and more resistant to physical stress.

How long do magnets last?

There isn’t a single expiry date for magnets. Instead, their lifespan depends on material, usage, and environment.

• Permanent magnets made of neodymium, ferrite, or samarium cobalt are designed to last indefinitely under ideal conditions. However, heat, vibration, and exposure to strong fields can shorten their working life.

• Ferromagnets, like iron and cobalt, provide strong magnetic fields but are vulnerable to high temperatures and corrosion.

• Diamagnetic and paramagnetic materials exhibit much weaker forms of magnetism and are less commonly used in practical applications.

Under everyday use, such as fridge magnets, toys, or household tools, magnets often retain useful strength for years or even decades. Industrial magnets, on the other hand, may degrade faster due to harsher operating conditions.

Can you remagnetise a magnet?

The good news is that weakened magnets aren’t always a lost cause. You can restore their strength using a few methods:

• Using a stronger magnet: Rubbing a powerful magnet over a weaker one in a single direction helps realign the weaker magnet’s domains.

• Using electric current: Wrapping a wire coil (called a solenoid) around the magnet and passing current through it generates a magnetic field, recharging the magnet.

• Professional remagnetisation: For large or specialised magnets, suppliers can use advanced equipment to restore full strength.

For small-scale projects or home experiments, the first two methods often work well. It’s a practical way to breathe new life into toy magnets, fridge magnets, or educational sets.

Conclusion

Magnets may not last forever, but understanding how they work and what causes them to weaken allows us to make the most of their fascinating properties. Heat, improper storage, and physical damage are the usual culprits behind their gradual decline, while careful use and maintenance can keep them functioning for many years. Even when a magnet weakens, it can often be remagnetised, ensuring it continues to play a role in science, industry, and everyday life. So, while they may not age as gracefully, magnets remain a remarkable reminder of the unseen forces shaping our world.

Just like how magnets can change over time, your child’s curiosity in science can grow stronger with the right guidance. At Heuristics Science, we help primary and secondary students in Singapore uncover the fascinating “why” behind natural phenomena through our proven TCR Answering Technique and hands-on applications. Join us today, and let’s make science not just a subject to study but also a world of discoveries waiting to be explored!