Copper is not magnetic in the conventional sense — a permanent magnet does not attract it. But copper does interact with magnetic fields in a physically interesting way: it is diamagnetic, which means it is weakly repelled by a magnetic field rather than attracted to it. It also generates strong eddy currents in changing magnetic fields, which is the basis for several practical engineering applications.
Understanding copper’s relationship with magnetism requires distinguishing three things that people often conflate: attraction to permanent magnets (which copper does not exhibit), magnetic susceptibility (which copper has, in a small negative quantity), and electromagnetic induction effects (which copper exhibits strongly due to its exceptional electrical conductivity).
Is Copper Magnetic? The Direct Answer
A permanent magnet placed near a piece of copper will not attract it. Copper contains no unpaired electrons that could align with an external magnetic field to produce a net magnetic moment — the mechanism behind ferromagnetism in iron, nickel, and cobalt. Copper’s electron configuration is [Ar] 3d¹⁰ 4s¹: the 3d subshell is filled, leaving no unpaired electrons in the d orbitals that dominate magnetic behavior in transition metals.
Copper is therefore classified as diamagnetic — one of three categories of magnetic behavior in materials:
| Magnetic type | Behavior in the field | Cause | Examples |
|---|---|---|---|
| Ferromagnetic | Strongly attracted; can retain magnetization | Unpaired electrons with aligned spins (exchange coupling) | Iron, nickel, cobalt, most steels |
| Paramagnetic | Weakly attracted; no retained magnetization | Unpaired electrons, random alignment without a field | Aluminum, titanium, platinum, manganese |
| Diamagnetic | Weakly repelled | All electron spins paired; induced opposing moment | Copper, gold, silver, zinc, bismuth |
Copper’s diamagnetism is extremely weak. Its volume magnetic susceptibility is χ = −9.7 × 10⁻⁶ (dimensionless, SI units). A negative susceptibility means the induced magnetization opposes the applied field — the definition of diamagnetic behavior. The magnitude (9.7 millionths) means the effect is so small it is unmeasurable without sensitive laboratory instruments.
Why Copper Is Diamagnetic — The Electron Structure Explanation
Paired electrons and Lenz’s law at the atomic scale
Every moving charged particle generates a magnetic moment. In atoms, electrons in orbitals each generate a magnetic moment from their orbital motion and from their intrinsic spin. When two electrons occupy the same orbital, their spins must be antiparallel (Pauli exclusion principle) — their magnetic moments exactly cancel.
Copper’s 3d¹⁰ subshell contains 10 electrons arranged in 5 filled orbitals, each pair with opposing spins. The 4s¹ valence electron is unpaired, which would normally suggest paramagnetism. However, in metallic copper, the 4s electrons form a conduction band shared across the crystal — they do not retain the localized unpaired spin character that produces paramagnetism. The net result is a small, negative (diamagnetic) susceptibility.
Diamagnetism itself arises from an induced effect described by Lenz’s law applied at the atomic scale: when an external magnetic field is applied, the field induces a small circular current in each electron orbit, and by Lenz’s law, the magnetic moment of that induced current opposes the applied field. This induced opposition is what produces the weak repulsion characteristic of diamagnetic materials.
Why the effect is so small
The induced diamagnetic moment is proportional to the area of the electron orbit and the applied field strength. Atomic electron orbits are on the order of 10⁻¹⁰ m — extremely small. The induced diamagnetic effect is therefore orders of magnitude smaller than the permanent magnetic moments produced by unpaired electron spins. Even in materials with significant unpaired spins (paramagnetic), the diamagnetic contribution is present but overwhelmed. Only in materials like copper, where unpaired spin moments are absent, does the diamagnetic term become the measurable net response.
The Magnetic Susceptibility of Copper vs. Other Engineering Metals
Magnetic susceptibility (χ) quantifies how strongly a material responds to an applied magnetic field. Positive χ = paramagnetic (attracted); negative χ = diamagnetic (repelled). Magnitude indicates the strength of the response.
| Metal | Susceptibility (χ × 10⁻⁶) | Classification | Notes |
|---|---|---|---|
| Bismuth (Bi) | −166.0 | Diamagnetic | Strongest diamagnetic pure metal |
| Silver (Ag) | −23.8 | Diamagnetic | Stronger than copper |
| Copper (Cu) | −9.7 | Diamagnetic | Non-magnetic to permanent magnets |
| Gold (Au) | −34.0 | Diamagnetic | Stronger than copper |
| Zinc (Zn) | −11.4 | Diamagnetic | Similar to copper |
| Lead (Pb) | −23.0 | Diamagnetic | Diamagnetic heavy metal |
| Aluminum (Al) | +20.7 | Paramagnetic | Weakly attracted; not measurable |
| Titanium (Ti) | +182 | Paramagnetic | Stronger paramagnetic response |
| Platinum (Pt) | +201 | Paramagnetic | Significant paramagnetism |
| Manganese (Mn) | +529 | Paramagnetic | Strong paramagnetism |
| Iron (Fe) | ~200,000 | Ferromagnetic | 20,000× stronger than Mn |
| Nickel (Ni) | ~600,000 | Ferromagnetic | Strongly magnetic |
Source: CRC Handbook of Chemistry and Physics, 104th Edition.
The key practical message from this table: aluminum is paramagnetic (positive susceptibility), meaning it is technically attracted to a magnetic field — but the attraction is so weak (χ = +20.7 × 10⁻⁶) that it is completely undetectable with any ordinary magnet. Neither copper’s diamagnetism (repulsion at −9.7 × 10⁻⁶) nor aluminum’s paramagnetism (+20.7 × 10⁻⁶) produces any force that would be noticeable in fabrication, handling, or ordinary use.
The distinction between “truly non-magnetic” materials (no response to magnets) and “weakly non-ferromagnetic” materials (technically paramagnetic or diamagnetic but undetectable in practice) is what matters for engineering. For any practical purpose — crane magnets, magnetic particle inspection, magnetic chucks, MRI compatibility — copper, aluminum, gold, silver, zinc, and lead are all effectively non-magnetic.
Copper and Changing Magnetic Fields: Eddy Currents
While copper has no meaningful response to static magnetic fields, it interacts strongly with changing magnetic fields through electromagnetic induction. This is the phenomenon that causes copper to appear “magnetic” in certain demonstrations and produces several practical engineering effects.
How eddy currents work in copper
When a magnetic field changes in the vicinity of a conductive metal, it induces circulating electrical currents — eddy currents — within the metal. By Faraday’s law, the changing magnetic flux induces an EMF, and the resulting current flows in closed loops within the conductor. By Lenz’s law, these currents are directed to oppose the change in flux.
Copper’s exceptional electrical conductivity (58 MS/m at 20°C — the second-highest of all metals after silver) means that for a given induced EMF, larger eddy currents flow in copper than in any other practical engineering metal. Large eddy currents produce large opposing magnetic forces.
The practical demonstrations of copper-magnet interaction:
Magnet through a copper tube: Drop a strong neodymium magnet through a copper tube. The magnet falls much more slowly than free-fall — it appears to float. The changing magnetic field as the magnet moves induces eddy currents in the tube wall; these currents create a magnetic field that opposes the magnet’s motion (Lenz’s law), producing a braking force proportional to velocity. This is electromagnetic braking with no physical contact.
Pendulum over copper plate: A copper pendulum swings over a strong magnet: no effect. A neodymium magnet pendulum swings over a copper plate: it brakes rapidly to a stop. The asymmetry illustrates that it is the changing flux through the conductor, not any attraction, that produces the force.
These demonstrations sometimes confuse observers into thinking copper is magnetic. It is not — the force is electromagnetic induction in a conductive non-magnetic material, not ferromagnetic attraction.
Practical eddy current applications in copper and metals
Eddy current braking: High-speed rail systems, roller coasters, and industrial machinery use copper or aluminum plates moving through a magnetic field gap to provide smooth, contactless deceleration. No friction, no wear, force proportional to velocity — the force automatically decreases as the object slows.
Induction heating: Alternating magnetic fields induce eddy currents in conductive metals, heating them resistively. Induction heaters and induction stovetops exploit this. Copper, being highly conductive, is actually less efficiently heated by induction than steel — the low resistivity means the same eddy current dissipates less power as heat (P = I²R). Steel’s higher resistivity heats more efficiently per unit current.
Eddy current non-destructive testing (NDT): Eddy current probes are used to detect cracks, thickness variations, and conductivity changes in conductive materials including copper, aluminum, and non-ferromagnetic stainless steel. This is distinct from magnetic particle inspection (MPI), which requires ferromagnetic materials.
Electromagnetic shielding: Copper’s high conductivity makes it an effective shield against electromagnetic interference (EMI). An alternating magnetic field induces eddy currents in a copper sheet that produce a counter-field, attenuating the original field on the far side. This is why copper is used for RF shielding in electronics enclosures, Faraday cages, and MRI room shielding.
Why Magnetic Properties Matter in Copper Fabrication
For fabricators and engineers working with copper, the magnetic properties produce three practical implications:
Magnetic lifting and handling. Electromagnetic crane magnets used to handle structural steel plate do not work on copper. This is not because copper is repelled — the diamagnetic repulsion force is immeasurably small at any achievable field strength — but because copper’s negligible permeability means the magnet cannot grip it. Copper sheet, copper bus bar, and copper tube must be handled with mechanical grabs, vacuum lifters, or strap slings. Experienced fabricators know this; engineers specifying material handling for mixed copper-steel facilities sometimes overlook it.
Magnetic chuck machining. Ferromagnetic steel parts are held on magnetic chucks during surface grinding and EDM operations. Copper workpieces cannot be held magnetically and require mechanical vices, adhesive mounting, or custom fixtures. This adds setup time and limits positioning flexibility compared to steel.
Laser cutting and plasma cutting implications. Neither fiber laser cutting nor plasma cutting is affected by the workpiece’s magnetic properties — the cutting energy is electromagnetic radiation or plasma arc, not a magnetically coupled force. Copper’s challenges in laser cutting (high reflectivity at 1,064 nm, high thermal conductivity) are thermal and optical, not magnetic. The full picture for cutting reflective metals, including copper, is covered in our guide to cutting reflective metals.
Learn more:
Engineer’s Guide: Is Stainless Steel Magnetic? Explaining Different Grades
Frequently Asked Questions About Copper and Magnetism
Q: Is copper magnetic?
No, not in the sense that a permanent magnet attracts it. Copper is diamagnetic — it has a volume magnetic susceptibility of −9.7 × 10⁻⁶, meaning it is infinitesimally repelled by a magnetic field. This effect is too small to be detectable without laboratory instruments. A magnet placed near copper produces no visible force. For all practical engineering purposes, copper is non-magnetic.
Q: Why does copper slow down a falling magnet inside a copper tube?
This is electromagnetic induction, not magnetism. The moving magnet’s changing magnetic field induces eddy currents in the copper tube. These eddy currents produce their own magnetic field that opposes the magnet’s motion (Lenz’s law). The result is a contactless braking force proportional to the magnet’s velocity. Copper is not attracted to the magnet — the eddy current braking force arises from copper’s exceptional electrical conductivity, not its magnetic susceptibility.
Q: Is brass magnetic?
No. Brass is a copper-zinc alloy, and both copper and zinc are diamagnetic. Common brass grades (C26000 to C28000) have magnetic susceptibility values similar to copper — essentially non-magnetic. Lead-bearing brass (C36000) is also non-magnetic; lead is diamagnetic (χ = −23 × 10⁻⁶). The addition of small amounts of paramagnetic elements like tin or manganese in some brass alloys does not produce measurable attraction to permanent magnets.
Q: Can you use a magnet to test if metal is copper?
Partially. A permanent magnet test correctly identifies that copper is not ferromagnetic — it will not be attracted. However, you cannot positively confirm a metal is copper by the magnet test alone, because many other non-ferromagnetic metals (aluminum, brass, bronze, austenitic stainless steel, titanium, zinc) also fail to attract a magnet. For positive copper identification, visual inspection (reddish color), density check (8.96 g/cm³), or XRF analysis is required.
Q: Is stainless steel magnetic?
It depends on the grade. Austenitic stainless steels (304, 316) are paramagnetic in the fully annealed condition — they are not attracted to permanent magnets. However, cold working (bending, drawing, machining) can induce a martensitic transformation in austenitic stainless, making it weakly ferromagnetic. Ferritic stainless steels (430) and martensitic stainless steels (410, 420, 440C) are ferromagnetic — they are attracted to magnets. For food processing, medical, and MRI-compatible applications, fully annealed austenitic grades are specified to ensure non-magnetic behavior.
Q: What metals are truly non-magnetic?
Metals that are neither ferromagnetic nor strongly paramagnetic — and therefore show no detectable attraction to permanent magnets under any ordinary conditions — include: copper, aluminum, gold, silver, zinc, lead, tin, titanium, brass, bronze, austenitic stainless steel (annealed), and most non-ferrous alloys. Among these, copper, gold, silver, and zinc are diamagnetic (technically repelled but immeasurably so); aluminum and titanium are paramagnetic (technically attracted but immeasurably so). All are “non-magnetic” for engineering purposes.
References
- Haynes, W.M., ed., CRC Handbook of Chemistry and Physics, 104th Edition. CRC Press, Boca Raton, FL, 2024. (Magnetic susceptibility data for all elements: copper χ = −9.7 × 10⁻⁶; bismuth, silver, gold, aluminum, titanium, and iron values; classification of diamagnetic, paramagnetic, and ferromagnetic behavior; electrical conductivity of copper 58 MS/m.)
- Kittel, C., Introduction to Solid State Physics, 8th Edition. Wiley, New York, 2005. (Quantum mechanical basis of diamagnetism: paired electron cancellation, Lenz’s law at the atomic scale, Langevin diamagnetic susceptibility formula; Pauli exclusion principle and magnetic behavior; eddy current physics in conductive metals.)
- ASTM B152/B152M, Standard Specification for Copper Sheet, Strip, Plate, and Rolled Bar, ASTM International, current edition. (Copper grade definitions C10100–C12200; purity classifications relevant to electrical conductivity and therefore eddy current applications; the material standard for commercial copper discussed in the fabrication section.)
- Griffiths, D.J., Introduction to Electrodynamics, 4th Edition. Pearson Education, Upper Saddle River, NJ, 2013. (Faraday’s law of electromagnetic induction; Lenz’s law; eddy current theory; electromagnetic braking force derivation; the physical basis for all eddy current effects described in the copper-magnet interaction section.)
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