Permanent magnets do lose their strength over time, though the rate depends enormously on the type of magnet, how it is used, and what it is exposed to. A high-quality neodymium magnet sitting on a shelf at room temperature might lose a fraction of a percent of its magnetization per decade, so little that you would never notice. But subject that same magnet to heat, physical impacts, corrosion, or strong opposing magnetic fields, and the loss can be dramatic and rapid. The word “permanent” in permanent magnet is relative, not absolute, and understanding why magnets weaken tells you a lot about how to keep them strong.
Why Magnets Weaken at All
Inside a magnet, tiny regions called magnetic domains are aligned so their fields point roughly the same direction. That alignment is what produces the external magnetic field you can feel. But alignment is not the lowest-energy state for every domain. Some domains are “eager” to flip back to a random orientation, and given enough energy or time, they will. The strength of a magnet depends on how stubbornly those domains resist flipping, a property engineers call coercivity. Magnets with high coercivity hold their alignment against bigger disturbances and for longer periods.
The domains most likely to flip first are the ones sitting at grain boundaries and near the edges and corners of the magnet’s internal crystal structure, where local demagnetizing fields are strongest. These internal fields effectively push back against the magnet’s own magnetization, and their influence is greatest in spots where the geometry creates sharp transitions between magnetized regions. Research on how magnetization reversal begins in permanent magnets has confirmed that these edge and corner regions are the weakest links, where the magnetic alignment first starts to break down.
Heat Is the Biggest Everyday Threat
Temperature is the most common reason magnets lose strength in real-world applications. Every permanent magnet has a maximum operating temperature beyond which it starts to lose magnetization irreversibly. Below that threshold, heating still causes a reversible loss: warm the magnet up and its field drops a bit, cool it back down and the field mostly returns. Above the threshold, some of the loss sticks.
For standard neodymium-iron-boron magnets, the reversible temperature coefficient is roughly negative 0.1% per degree Celsius between room temperature and 100°C. That means for every degree the magnet heats up, it temporarily loses about a tenth of a percent of its field strength. Over a range of 80°C, that adds up to a noticeable drop. Researchers have found that partially replacing iron with cobalt in neodymium magnets can shrink this coefficient dramatically, from around negative 0.116% per degree down to about negative 0.028% per degree, which is even better than samarium-cobalt magnets, a material long prized for thermal stability.1Elsevier / Journal of the Less Common Metals. Rare-earth-transition-metal-boron permanent magnets with smaller temperature coefficients The trade-off is that cobalt substitution can reduce other magnetic properties, so magnet manufacturers balance thermal stability against raw strength depending on the application.
Every magnet type also has a Curie temperature, the point at which thermal energy overwhelms all magnetic order and the material stops being a magnet entirely. For neodymium magnets the Curie temperature is around 310°C, for ferrite magnets around 450°C, and for samarium-cobalt magnets around 700–800°C. You would not encounter these temperatures in everyday life, but motors, generators, and industrial equipment can get surprisingly hot under load.
Physical Impact and Vibration
Dropping a magnet, hammering it, or subjecting it to repeated vibration can knock domains out of alignment. This is not folk wisdom; it has been measured in controlled experiments. Research on the magnetization of unexploded ordnance found that shock demagnetization is real and scales with impact severity: objects with medium and high initial magnetization all lost some of their magnetic remanence when subjected to controlled impacts, with more demagnetization at higher impact velocities.2Journal of Applied Geophysics. Experimental measurements of shock induced changes to the magnetization of unexploded ordnance
The mechanism has been studied in detail with neodymium magnets exposed to shock waves. Under high-pressure impacts, the coercivity of NdFeB magnets can plummet, dropping from around 21.4 kOe to just 3.2 kOe in one set of experiments. The cause turns out to be a chaotic reorientation of the crystal grains inside the magnet, essentially scrambling the very structure that keeps the domains aligned.3Chinese Physics Letters. The Impact Induced Demagnetization Mechanism in NdFeB Permanent Magnets The good news from that same research is that the damage can be reversed with careful heat treatment: annealing the compressed magnets at 900°C and then 520°C restored the coercivity, suggesting the crystal structure itself was not destroyed, just disordered.
Studies on natural magnetite subjected to shock waves paint a similar picture at a broader range of pressures. Up to about 10 GPa, the dominant effect is brittle fragmentation of the grains, which changes the magnetic domain structure and lowers the overall magnetization. At even higher pressures, around 20 GPa, a partial recovery begins because the intense shock heating anneals the material somewhat. But by 30 GPa, the lattice damage becomes so severe that magnetization drops sharply again.4Geochemistry, Geophysics, Geosystems. Shock‐induced deformation phenomena in magnetite and their consequences on magnetic properties For everyday purposes, you do not need to worry about gigapascal pressures, but the principle scales down: even modest repeated impacts, like a magnet repeatedly snapping against a metal surface, can slowly chip away at its field strength over years.
Corrosion Eats Neodymium Magnets From the Inside
If you have ever seen a neodymium magnet with a bubbling, flaking coating, you have seen corrosion in action. NdFeB magnets have notoriously poor corrosion resistance compared to ferrite or samarium-cobalt types, and the mechanism is particularly destructive. The neodymium-rich phase that sits between the magnetic grains is chemically reactive. When exposed to moisture, this intergranular phase dissolves rapidly because of the electrochemical mismatch between it and the surrounding magnetic grains. As it dissolves, the ferromagnetic grains physically detach from one another. Making things worse, the corroding neodymium absorbs hydrogen gas produced during the corrosion reaction, which causes the intergranular phase to swell. That expansion creates cracks, and in severe cases the magnet literally crumbles into powder.5Elsevier. Corrosion, passivation and breakdown of passivity of neodymium
This is why virtually all commercial neodymium magnets come with a protective coating, usually nickel-copper-nickel plating, epoxy, or sometimes zinc or gold. If that coating is scratched or chipped, moisture can reach the underlying material and the degradation begins. Magnets used outdoors, in high-humidity environments, or submerged in water are at particular risk. Ferrite magnets, by contrast, are ceramic and essentially immune to corrosion, which is one reason they remain popular for applications where the magnet will be exposed to harsh conditions despite their much lower strength.
Opposing Magnetic Fields
Placing a magnet near a strong opposing magnetic field can partially demagnetize it. This happens in electric motors and generators, where magnets sit inside coils that produce alternating fields. Each cycle of the alternating field nudges a few more domains out of alignment. Engineers design around this by choosing magnet grades with enough coercivity to resist the peak opposing fields the motor produces, but a magnet running near its limits in a motor that gets hot will lose strength faster than one with generous margins.
Even placing two magnets next to each other in a repelling orientation can cause some demagnetization if they are left that way for long periods, particularly if the magnets are thin or have a low length-to-diameter ratio. The shape of a magnet matters because it determines how strong the internal demagnetizing field is. Short, flat magnets have higher internal demagnetizing fields than long, cylindrical ones. Research on magnetization reversal in permanent magnets has shown that this self-demagnetizing field is strongest near the edges and corners of the grain structure, so magnets with unfavorable geometries are inherently more vulnerable.6Elsevier / Scripta Materialia. Searching the weakest link: Demagnetizing fields and magnetization reversal in permanent magnets
Radiation Damage in Specialized Settings
For most people, radiation is not a concern for their magnets. But in particle accelerators, medical imaging equipment, and space applications, magnets can be exposed to significant doses of gamma rays, neutrons, or high-energy electrons. Neodymium magnets are particularly sensitive to radiation damage. Studies on magnets used in insertion devices for synchrotron light sources have measured the effects directly: untreated NdFeB magnet samples showed drastic demagnetization when irradiated, while samples that had been thermally annealed beforehand fared much better, losing less than 1% of their magnetization.7Elsevier / Radiation Measurements. Radiation damage in permanent magnets for ID Facilities that use permanent magnets in high-radiation environments select special high-coercivity grades and sometimes pre-treat them thermally to improve radiation hardness.
How Quickly Does a Magnet Lose Strength Just Sitting Around?
If you protect a high-quality neodymium magnet from heat, corrosion, impacts, and opposing fields, the natural aging process is extremely slow. The loss comes from what physicists call magnetic viscosity, the gradual, thermally driven reorientation of the least-stable domains. At room temperature, modern sintered NdFeB magnets lose something on the order of a few hundredths of a percent of their remanence per year. Over a human lifetime, that adds up to a loss so small it would be hard to measure without laboratory instruments.
Ferrite magnets age a bit faster in percentage terms but start from a much lower baseline strength. Samarium-cobalt magnets are exceptionally stable over time and at elevated temperatures, which is why they are still used in aerospace and military applications despite costing more and being weaker per unit volume than neodymium types. Alnico magnets, the horseshoe magnets of science-class fame, have extremely low coercivity by modern standards, meaning they are easily demagnetized by stray fields or physical mishandling, even though the base material is quite thermally stable.
The evolution of magnet materials over the past century has been striking. In 1917, KS Steel magnets achieved an energy product of about 1 MGOe. By the early 1980s, energy products had risen by a factor of 50 and intrinsic coercivity by a factor of 100. Modern sintered NdFeB magnets can reach commercial energy products as high as 52 MGOe.8ScienceDirect (Woodhead Publishing). Chapter 1 – The history of permanent magnets That hundredfold increase in coercivity is directly relevant to longevity: today’s magnets resist demagnetization far more effectively than those from even a few decades ago.
Can You Restore a Weakened Magnet?
It depends on why the magnet weakened. If the loss came from heat exposure or impact that disordered the domains without destroying the crystal structure, remagnetization is usually possible. Industrial magnetizers use strong pulsed fields, typically many times stronger than the magnet’s own coercive field, to snap the domains back into alignment. For many applications, this is routine: manufacturers of motors and sensors remagnetize components as part of quality control.
Thermal remagnetization, where a weakened magnet partially recovers its strength when cooled back down after heating, is a well-documented phenomenon. Careful studies of samarium-cobalt magnets in closed circuits have observed thermal remagnetization recovering more than 80% of the saturation magnetization after heating.9Elsevier (Journal of Magnetism and Magnetic Materials). Theory of thermal remagnetization of permanent magnets The degree of recovery depends on the magnet material, the shape (which determines how strong the self-demagnetizing field is), and whether the magnet is in a circuit with other magnetic materials that help guide the field.
If the magnet has corroded and the grains have physically separated, no amount of remagnetization will help. The structure is gone, and you need a new magnet. Similarly, if the crystal lattice itself has been severely damaged by extreme shock or radiation, remagnetization alone will not restore the original performance, though annealing at high temperatures can sometimes repair enough of the structure to bring back useful levels of magnetism.
Practical Tips for Keeping Magnets Strong
Most of the magnet degradation people encounter is avoidable. A few guidelines cover the majority of situations:
- Avoid heat: Keep magnets away from engines, stoves, soldering irons, and direct sunlight in enclosed spaces. Standard neodymium grades start to lose irreversible magnetization above about 80°C. If your application runs hot, ask for a high-temperature grade.
- Protect the coating: For neodymium magnets, a chipped or scratched coating is the beginning of corrosion. Handle them carefully, and do not let them slam together at full speed, which can chip the plating and also cause impact demagnetization.
- Store with a keeper: Alnico and other low-coercivity magnets benefit from being stored with a steel keeper bar across the poles, which reduces the internal demagnetizing field. Modern neodymium and ferrite magnets generally do not need keepers, but storing magnets in attracting pairs rather than repelling orientation is still good practice.
- Mind the geometry: Thin disc magnets magnetized through their thickness have higher self-demagnetizing fields and are slightly more vulnerable to gradual loss than longer magnets magnetized along their length. If longevity matters, favor shapes where the magnetization direction is the long axis.
What Rocks and the Moon Tell Us About Long-Term Magnetism
Some of the most vivid evidence for magnets losing strength over time comes not from engineering labs but from geology. Rocks containing magnetite grains record the Earth’s magnetic field at the time they formed or were last heated. Over thousands to millions of years, those original magnetic signals fade as a secondary magnetization, called viscous remanent magnetization, slowly accumulates in the direction of the current ambient field. Researchers have used this phenomenon to date geological events: by measuring the temperature at which the viscous component is erased in the lab, they can estimate how long a rock has sat in its current position.10Geophysical Research Letters. Unblocking temperatures of viscous remanent magnetism in displaced granitic boulders, Icicle Creek glacial moraines (Washington, USA)
Lunar rocks tell an even more interesting story. Studies of Moon samples brought back by the Apollo missions revealed two distinct types of magnetic aging. Igneous lunar rocks, whose magnetic properties come from relatively large grains of metallic iron, show weak but extremely persistent magnetic viscosity: the decay of their magnetization continues for a very long time after even brief exposure to a field. Lunar soils and lightly processed breccias, which contain much finer iron particles, behave differently, acquiring an unusually strong viscous magnetization that decays on a timescale roughly equal to how long it was exposed to a field.11Reviews of Geophysics. Theory of the magnetic viscosity of lunar and terrestrial rocks The grain size and internal structure of the magnetic particles determine which behavior dominates, a principle that applies just as much to engineered magnets as to Moon dust.
Within engineered magnets, the internal grain structure is carefully controlled during manufacturing to maximize coercivity and, by extension, long-term stability. Techniques like precipitation hardening create microscopic obstacles that pin domain walls in place, preventing them from moving in response to thermal fluctuations or external disturbances. Research on NdFe11Ti-based alloys has shown that the nature of this pinning changes with the alloy composition: at lower additive fractions, a weak pinning mechanism dominates, while at higher fractions, strong pinning takes over, dramatically increasing the force needed to shift a domain wall.12Journal of Applied Physics. Domain wall pinning in precipitation hardenable NdFe11Ti-based high coercivity magnet alloys This kind of microstructural engineering is one of the reasons modern permanent magnets are so much more durable than their predecessors, and why the practical answer to “do magnets wear out?” has shifted from “yes, fairly easily” to “only if you mistreat them.”