Magnets are widely used in everyday life. While permanent magnets are engineered to retain their magnetic properties for extended periods, various factors can cause them to weaken or lose strength. This gradual degradation is a natural process influenced by environmental and physical interactions.
Understanding Magnetism
To understand how magnets lose strength, it helps to know the basis of magnetism. Magnetic materials contain microscopic regions called magnetic domains. Each domain acts like a tiny magnet. In an unmagnetized state, these domains are randomly oriented, with their individual magnetic fields canceling each other out.
When a material becomes magnetized, these domains are largely aligned in a common direction. This alignment creates a net magnetic field that extends beyond the material, giving it its magnetic properties. The strength of the magnet depends on the degree of alignment among these domains. Permanent magnets, such as those made from neodymium or ferrite, have domains that are difficult to dislodge from this aligned state, allowing them to retain magnetism for long periods.
In contrast, temporary magnets, like soft iron, are easily magnetized but also lose their alignment and magnetism quickly once an external magnetic field is removed. This difference in domain stability distinguishes permanent from temporary magnets, and is key to a magnet’s lasting power.
Factors That Reduce Magnet Strength
Several factors reduce a magnet’s strength over time.
Heat
Exposure to heat is a significant cause. As a magnet’s temperature rises, the atoms within its structure vibrate more intensely, disrupting the orderly alignment of the magnetic domains. This increased thermal energy causes the domains to become disoriented. Each magnetic material possesses a specific Curie temperature, above which it completely loses its permanent magnetism. Exceeding this temperature randomizes the magnetic domains, leading to loss of magnetism.
Physical Shock
Physical shock or impact can diminish a magnet’s power. A sudden, strong blow or repeated impacts can mechanically dislodge or misalign the delicate orientation of the magnetic domains. This physical disruption reduces the overall collective magnetic field, weakening the magnet. The material’s internal magnetic structure becomes compromised.
External Magnetic Fields
Strong external magnetic fields present another threat. If a permanent magnet is placed within a powerful magnetic field that opposes its existing domain alignment, it can force the domains to reorient or even reverse their polarity. This can significantly weaken or demagnetize the magnet.
Environmental Factors
Environmental factors like corrosion or oxidation can also play a role over extended periods. Chemical reactions with the environment can degrade the magnet’s material. For example, some rare-earth magnets are coated to prevent such degradation.
Natural Decay
Magnets experience a very slow, natural decay of strength over time, even under ideal conditions. This intrinsic magnetic decay is often negligible for practical purposes. It is due to the inherent thermal energy within the material, causing minute, continuous domain disalignment.
Preserving Magnetic Power
Understanding factors that weaken magnets allows for practical preservation steps.
Avoid Heat
To prevent thermal demagnetization, avoid exposing magnets to extreme heat sources. Keeping them away from direct sunlight, hot machinery, or open flames helps maintain their internal domain alignment.
Prevent Physical Shock
Protecting magnets from physical shock is important. Dropping a magnet or allowing it to collide forcefully with other hard surfaces can cause internal damage to its magnetic structure. Handling magnets with care and storing them in protective casings can mitigate this risk.
Proper Storage
Proper storage is another consideration for maintaining magnetic strength. Magnets should be kept away from strong external magnetic fields, such as those generated by motors or other powerful magnets. For pairs of magnets, storing them with “keepers” (pieces of soft iron placed across their poles) or ensuring like poles do not face each other can prevent self-demagnetization.
Protect from Environment
Safeguarding magnets from moisture and corrosive environments can prolong their lifespan. Many magnets, especially those made from rare-earth elements, are susceptible to corrosion, which can degrade the material over time. Storing them in dry conditions or using coated magnets can help prevent this environmental damage.
Can Magnetism Be Restored?
When a permanent magnet loses strength, it can often be re-magnetized. This process involves exposing the magnet to a very strong external magnetic field. The powerful external field effectively realigns the magnetic domains within the material, restoring its magnetic properties.
Re-magnetization is typically achieved using specialized equipment, such as powerful electromagnets or very strong permanent magnets. The success of this process depends on several factors, including the original material of the magnet, the extent of its demagnetization, and the strength of the re-magnetizing field applied. While possible, complete restoration to original strength is not always guaranteed, particularly if the magnet has suffered significant structural damage or extreme demagnetization.
For most commercial or industrial applications, re-magnetization is a specialized process often performed by professionals with the appropriate high-field equipment. For smaller, less critical magnets, sometimes exposure to a much stronger magnet can impart some degree of renewed magnetism. This capability highlights that the magnetic potential within the material remains, even if its organized structure is disrupted.