Every way of demagnetizing a magnet comes down to scrambling its internal order so its pull cancels itself out. The three practical routes are heat, a fading alternating magnetic field, and physical shock.1Maurer Magnetic. Demagnetization – Basics and Know-How | Maurer Magnetic AG They differ a lot in how complete and how safe they are, and the right one depends on what the magnet is made of.
What Actually Happens When a Magnet Loses Its Magnetism
A magnet is made of tiny magnetic regions called magnetic domains, and its pull comes from them pointing the same way. Demagnetizing means pushing those domains into an even, random disorder, ideally broken into the finest structure possible.2Maurer Magnetic. Demagnetization – Basics and Know-How Domains pointing in random directions cancel each other, so the magnet’s outside field drops toward zero.
How hard that is depends on coercivity, a material’s resistance to changes in its magnetism. Spec sheets list it as the field needed to reduce the magnetism to zero.3Ideal Magnet Solutions. Understanding Coercivity Neodymium magnets have the highest coercivity of the common types, so they resist demagnetizing most.4Ideal Magnet Solutions. Understanding Coercivity Alnico magnets sit at the other end. Their coercivity is low, and they can lose strength just from being placed next to another alnico magnet in repulsion.5Dexter Magnetic Technologies. Frequently Asked Questions A weak alnico or a magnetized steel screwdriver is easy to erase, while a neodymium magnet takes heat or very strong equipment.
That split matters because a screwdriver or pair of tweezers that picked up magnetism is soft steel, and soft steel gives it up easily. Permanent magnets are built to resist erasing. The same method can work instantly on one and barely touch the other, so work out which you have before choosing.
Method 1, Heat the Magnet Past Its Curie Temperature
Heat randomizes aligned domains and breaks the magnet’s order.6Wikipedia. Curie temperature Above a point called the Curie temperature, a material loses its magnetic order entirely.7Journal of Magnetism and Magnetic Materials. The role of demagnetization factor in determining the ‘true’ value of the Curie temperature Steel heated past that point and then cooled is left with no leftover magnetic field.8NDE Ed. Demagnetization The Curie point differs by material:
- Neodymium magnets: about 310–400°C (590–752°F).9Wikipedia. Curie temperature
- Strontium ferrite (ceramic) magnets: about 450°C (842°F).10Wikipedia. Curie temperature
- Alnico magnets: about 700–860°C (1292–1580°F).11Wikipedia. Curie temperature
- Samarium-cobalt magnets: about 720–800°C (1328–1472°F).12Wikipedia. Curie temperature
- Low carbon steel: 770°C (1390°F).13NDE Ed. Demagnetization
Partial heating only weakens. Every magnet grade also has a maximum operating temperature printed on its spec sheet, and it sits well below the Curie point, because damage starts long before the magnetic order disappears. Go past that limit and some domains stay misaligned, so the magnet is weaker after cooling.14Strong Magnets GmbH. Avoid demagnetization: Tips & Causes Stay under it and the magnet generally recovers most of its strength as it cools.
In one test, neodymium magnets held at 400°C for 15 minutes were fully demagnetized.15PubMed Central. Effects of Thermal Demagnetization in Air on the Microstructure and Organic Contamination of NdFeB Magnets Larger magnets may need longer to heat through.16PubMed Central. Effects of Thermal Demagnetization in Air on the Microstructure and Organic Contamination of NdFeB Magnets Heating neodymium in air lets oxygen, carbon and zinc contaminate it, so keep the heating time short.17PubMed Central. Effects of Thermal Demagnetization in Air on the Microstructure and Organic Contamination of NdFeB Magnets
At home, a kitchen oven usually tops out near 260°C, too low to fully erase neodymium. A kiln, forge, or heat-treat oven gives reliable results. Heat the magnet evenly, handle it with tongs, and set it on a heat-proof surface. Let it cool slowly, away from other magnets, so it doesn’t pick up a field again.
The method has downsides. The coating can burn or blister, and the magnet may oxidize and lose material. It also rules out any watch or tool with heat-sensitive parts.
Method 2, Use a Fading Alternating Magnetic Field
An alternating field that steadily decreases flips the domains’ direction over and over, a little less each time, and the material ends up in a non-magnetized state.18TDK. How to Demagnetize a Magnet: 3 Effective Methods A device that does this is called a degausser, also sold as a demagnetizer. The fade comes either from turning the field down or from slowly pulling the object away from it.
The fade is the key part. If the field is cut while it’s at full strength, the object is left magnetized in whichever direction the field pointed at that instant. That’s why the slow lift-away matters: distance from the coil is what weakens the field, so a jerky or short motion doesn’t give a smooth fade. The object ends up near zero rather than reversed, which a plain opposing magnet can’t reliably achieve.
A watch makes a good worked example. Mechanical watches pick up magnetism and are fixed with a small watch demagnetizer that makes an alternating field.19Teddy Baldassarre. How to Demagnetize A Watch Place the watch dial-down on the pad or just above it, then press and hold the button.20Teddy Baldassarre. How to Demagnetize A Watch Keeping the button held, slowly lift the watch straight up and away.21Teddy Baldassarre. How to Demagnetize A Watch After about 30 cm (a foot), release the button and set the watch down.22Teddy Baldassarre. How to Demagnetize A Watch
Some mistakes leave the object magnetized. Releasing the button while the object is still on the pad can re-magnetize it. Moving too fast leaves leftover magnetism, so repeat a pass if the object still picks up pins. Small degaussers usually won’t fully erase strong neodymium magnets. Another field method applies an opposite-polarity field just past the reversal point and then stops.23Maurer Magnetic. Demagnetization – Basics and Know-How | Maurer Magnetic AG It only lands near zero if the field strength is set precisely, so it suits industrial equipment rather than home use.24Maurer Magnetic. Demagnetization – Basics and Know-How | Maurer Magnetic AG
Method 3, Physical Shock and Impact
Hard blows like hammer strikes can lower a magnet’s magnetism slightly.25Maurer Magnetic. Demagnetization – Basics and Know-How | Maurer Magnetic AG Impacts throw the material’s internal structure into disorder.26Journal of Alloys and Compounds. Magneto-mechanical properties of sintered NdFeB under impact load: Impact-induced demagnetization experiment, constitutive model and micromagnetic simulation Under extreme shock-wave pressure, neodymium magnets’ resistance to demagnetizing fell from about 21.4 to 3.2 units, a drop of about 85%.27Chinese Physics Letters. The Impact Induced Demagnetization Mechanism in NdFeB Permanent Magnets That took industrial shock compression, far beyond any hammer.28Chinese Physics Letters. The Impact Induced Demagnetization Mechanism in NdFeB Permanent Magnets
At home it’s a poor choice. Rare-earth magnets are brittle, and striking or crushing them should not be used to demagnetize.29Radial Magnets. How To Demagnetize A Magnet: 6 Methods That Work Hammering a neodymium magnet is more likely to chip it than erase it. Soft steel and alnico respond better, and a few sharp knocks can noticeably weaken a magnetized steel tool. Shards of neodymium can fly and cut skin or eyes, so wear safety glasses if you try this at all. Shock suits only a slightly magnetized nail or bit, and it isn’t suitable for watches or precision parts.
Which Method Works Best for Your Magnet
For magnetized steel tools and watches, a fading alternating field is the clean, safe choice.30TDK. How to Demagnetize a Magnet: 3 Effective Methods For neodymium magnets you want gone completely, heating above about 310–400°C is the dependable route.31Wikipedia. Curie temperature Alnico can be weakened by opposing fields alone, even another alnico in repulsion.32Dexter Magnetic Technologies. Frequently Asked Questions Ceramic, neodymium and samarium-cobalt magnets usually see very small permanent changes from such fields.33Dexter Magnetic Technologies. Frequently Asked Questions
Identifying the magnet comes first. Silver, very strong small magnets are often neodymium. Dark gray, brittle ones are often ceramic ferrite. Horseshoe and old red-painted magnets are often alnico. Looks are only a rough guide. Product listings or packaging may give a grade like N42.
A watch needs a watch demagnetizer and no heat, since the movement has parts heat can damage. A screwdriver, bit, or tweezers calls for a degausser. A strong permanent magnet you want fully erased calls for heat matched to the Curie point for its type.
Sometimes disposal is easier. A heavily coated neodymium magnet may not survive heating well. If you only want it to stop sticking, wrapping or enclosing it may be simpler. Magnet recyclers accept rare-earth magnets.
Accidental Demagnetization and How to Prevent It
Permanent magnets normally keep their field but can lose it to high heat, collisions, loss of material, and opposing fields.34Dura Magnetics. Causes of Demagnetization in Magnets Opposing fields can come from nearby current-carrying wires or from contact with other magnets or iron.35ADAMS. Top Causes of Permanent Magnet Demagnetization & Strength Loss Neodymium magnets also corrode readily in humidity and acidic liquids.36Corrosion Science. Effect of magnetization state on the corrosion behaviour of NdFeB permanent magnets Hydrogen from corrosion causes swelling, cracks, and crumbling.37Corrosion Science. Effect of magnetization state on the corrosion behaviour of NdFeB permanent magnets Rust and lost material directly reduce the magnet’s strength.38Journal of Magnetism and Magnetic Materials. Long-term effects of electrochemical corrosion on magnetic properties of sintered NdFeB magnets Signs of weakening include a fridge magnet that holds fewer sheets than before, coating flaking or rust spots on neodymium, and a speaker or motor magnet that performs poorly.
To prevent it, keep magnets below their maximum operating temperature. Store neodymium magnets dry and keep their coating intact. Store alnico magnets with keepers and avoid placing them in repulsion.39Dexter Magnetic Technologies. Frequently Asked Questions Stack magnets attracting rather than repelling, keep them away from stoves, car dashboards, and other hot spots, and use plastic spacers to avoid chipping collisions.
Can a Demagnetized Magnet Be Restored
A magnet weakened by heat or an opposing field stays weaker after cooling until it is re-magnetized.40Strong Magnets GmbH. Avoid demagnetization: Tips & Causes Once cooled, its domains can be realigned with a strong field to restore strength.41Applied Magnets Superstore. Can neodymium magnet be magnetized again after overheating and lost magnetism Corrosion loss can’t be undone, since most of the strength loss comes from lost magnet material.42Journal of Magnetism and Magnetic Materials. Long-term effects of electrochemical corrosion on magnetic properties of sintered NdFeB magnets Rare-earth magnets need a strong pulse magnetizer, not another magnet, and magnet suppliers and repair shops offer recharging. Stroking with a strong magnet can recharge steel and weak alnico. Overheated magnets with oxidized surfaces may not fully recover.
Checking Your Results and Staying Safe
Industrial inspectors use a gauss meter and treat less than 2 gauss of leftover magnetism as demagnetized.43Magnetic Products and Services. Magnetic Particle Inspection ‘Made Easy’ with the MPS Auto Degauss Magnetic field meters are sold for checking parts in welding shops.44ewm-group.com. Degaussing of components for reliable welding in day-to-day work At home, if the object no longer picks up pins or paper clips, it’s demagnetized enough for most uses. Dip the end in a pile of staples or pins, hold a compass near it to spot leftover fields, or compare it against an untreated identical magnet.
On safety, don’t heat coated permanent magnets with an open flame.45Radial Magnets. How To Demagnetize A Magnet: 6 Methods That Work Keep strong fields away from electronics, magnetic storage, and medical devices like pacemakers.46Radial Magnets. How To Demagnetize A Magnet: 6 Methods That Work Use fixtures and guarding with large magnets and follow equipment safety instructions.47Radial Magnets. How To Demagnetize A Magnet: 6 Methods That Work
Degaussers erase hard drives and tapes but have no effect on solid-state drives.48IT Asset Management Group. Hard Drive Destruction Methods + NIST 800-88 Compliance A degausser near a laptop with a hard drive can wipe data, and bank cards’ magnetic stripes can be erased too, though a strong field can still damage other electronics. Move phones and cards away before you use one.