Fact Check: Copper is a Magnetic Material?

In the high-speed, international metal recycling and precision electronics manufacturing market, a simple assumption or misconception can result in thousands of dollars in unnecessary lost value to a potential client for a single delivery or purchase order. One of the many stress points in the world of commodity purchasing and quality assurance arises from what is commonly referred to as the “magnet test.” Suppliers of copper cathodes and copper electrical scrap assure buyers that their products have not been contaminated with iron, which makes sense, given the extreme repulsion of iron to magnets and its common lack of inclusion in pure copper scrap products. Many times, however, a magnet will still pick up some products labeled copper and subsequently cause the buyer to wonder whether copper itself is a ferromagnetic metal, which therefore would still attract or at least be attracted to other magnets under some conditions.

Inadequate identification of the magnetic properties of materials in your inventory can result in rejection of entire shipments and can potentially cause catastrophic damage to induction furnaces and other pieces of highly specialized and expensive equipment, such as medical imaging devices. Effective trading of red metals globally requires an understanding of more than just the surface characteristics of copper and its behavior in magnetic fields.

The Scientific Reality: Copper is a Magnetic Material?

For the record, the answer is: no. Unlike iron and nickel, which are the metals that most people are familiar with when they hear of “magnetic,” copper is diamagnetic, not ferromagnetic, which means it is not generally considered “magnetic” in the traditional sense of the word. The ferromagnetism is the property of metals that most people mean when they talk about something being “magnetic.” Diamagnetism, the magnetic effect being described here, is a much weaker effect.

A diamagnetic material will be repelled by an applied magnetic field in the opposite direction. So, if you wave a very powerful Neodymium magnet towards a pure copper bar, it will repel it. Not a great amount, but repel it it will. So here is the first line of defense for our International Trader in protecting his shipment of precious metals. If a component is attracted to a magnet, red flags should wave bigly that there is iron or steel contamination in the component, despite the colour appearing to be within the Copper, Brass, and Bronze Guide.

Eddy Currents: Why People Think Copper is a Magnetic Material

Apparently, everyone’s videos and workshop demos prove that copper is a magnetic material, despite copper being diamagnetic and a magnet not being attracted to it. The reason that you see demos of magnets slowly falling through a copper pipe is because of Lenz’s Law and Eddy Currents.

In my work as a procurement specialist, I am learning that magnets and copper have a very interesting relationship. When a magnet is moved relative to a copper object, an electric current is generated in the copper. This current generates a magnetic field that acts to counteract the motion of the magnet. This is known as “magnetic braking” and is used on some of the more advanced industrial sorting systems for non-ferrous metals and recyclables. What is important to remember in this relationship is that it only occurs when something is moving. A stationary magnet and a stationary piece of copper will never attract each other.

Comparing Conductivity: Copper vs. Specific Heat of Aluminum in Magnets

This is part 1 in a series exploring why coil design engineers have to choose between copper and aluminum. The short answer is neither is a magnetic material. The longer answer is that choosing copper over aluminum or vice versa depends on many factors based on their properties and behavior in a magnetic field.

If the electrical conductivity of copper is higher than that of aluminum, the copper current induced by the alternating magnetic field is more important and therefore generates more eddy currents. This means that more heat is generated. Although copper has a lower specific heat (0.385 J/g·C) than aluminum (0.900 J/g·C), it is still hotter and is better dissipated. In B2B transformer winding and motor rotor trading, the selection between aluminum and copper “non-magnetic” metals is entirely based on heat dissipation requirements.

The Impact of Alloying: When Copper Becomes Magnetic

Cobalt fraud in copper products is perhaps the most dangerous and sophisticated in international trade. Such a thing is commonly referred to as “dirty alloy” . Pure copper is a non-magnetic material, while pure elements and many alloys (such as brass) are not attracted by magnets. However, a majority of copper alloys can be somewhat magnetic when the material contains certain impurities.

Monel Alloys: These are alloys that generally contain copper and nickel. They can be magnetic at room temperature if they contain sufficient nickel.

Beryllium Copper Non-sparking tools are most frequently made from Beryllium Copper, which is a copper alloy containing nickel and a small addition of Be. If the iron content in the alloy is not tightly controlled during the casting of the non-sparking tools, they may become slightly magnetised, which could cause a problem in the vicinity of an MRI.

Contaminated Scrap The major contaminating scrap in the secondary market is “No. 1 Burnt Copper,” which often contains steel bits from motor armatures.

If your “copper” scrap is magnetic, the melting points of the brass and steel contaminants that are present will start to become an issue. Iron can quite significantly affect the electrical conductivity of the copper, even at levels as low as 0.5%, depending on the specification of the final product.

Investigating the Melting Point of Copper and Magnetic Stirring

In the foundry stage of production, the matter of magnetism and copper becomes highly professional. To heat the copper to the melting point (1,085°C) in the induction furnace, which is widely used in today’s metal production, you need highly powerful and rapidly changing magnetic fields.

Because of the high conductivity of copper, the magnetic field generates huge current streams that, from the inside out, melt the metal. The magnetic field also stirs the metal electrically. We argue that copper is not a ferromagnetic material in the sense that it attracts the magnetic field. What is essential here is that it can be controlled in its liquid state in order to produce ultra-pure oxygen-free copper (OFC) that is used for the international electronics business.

Using the Color Guide to Copper, Brass, and Bronze to Spot Forgeries

Copper is a bit on the pricey side, so a lot of times you will run into copper-plated steel or zinc. The magnet test will still be a great tool to test, but pair that with a visual test and you’ll be okay. Check out our color guide to copper, brass, and bronze. Pure copper has a salmon-pink reddish color.

Pure Copper: Non-magnetic. Reddish hue.

Brass: Non-magnetic. Yellowish/Gold hue.

Bronze: Non-magnetic. Brownish/Dull gold.

Copper-Plated Steel: Magnetic. A common fastener and coin counterfeiting method.

Magnetic copper products are often base metals with a copper wash. Our International traders need to catch this out as early as possible, as the reverse is almost impossible to achieve, and returns from overseas are a major logistical headache.

The Steel Melting Temperature and Its Relation to Copper Contamination

In the steel industry, copper is often considered a tramp element. In the process of manufacturing steel by melting scrap steel, if the copper is not melted and taken out of the steel bath while the steel is heated to its melting temperature (approx. 1370°C – 1540°C), it can cause a condition known as “hot shortness”.

Copper, being a non-oxidizing element to iron, is not removed in the steel-making process. As copper has a tendency to be at the grain boundaries, and has a lower melting point than the finished steel, it remains as a liquid on the surface of the steel as it is rolled into a usable shape. This is why the magnetic separation process is so important; there must be no copper present in the molten steel. The fact that copper is not a magnetic piece, but it would not be picked up in the normal magnetic pulleys (as they attract only the iron-containing items), makes this part of the separation process even more important.

Frequently Asked Questions (FAQs)

Is copper ever magnetic?

Technically, no. Copper is diamagnetic, meaning it slightly resists magnetic fields. It is common to incorrectly believe copper to be magnetic due to either the eddy current effect, which generates a tiny temporary current while copper is moved through a magnetic field, or due to the presence of iron impurities within the copper.

Why does a magnet fall slowly through a copper pipe?

That is because of the eddy currents. The moving magnet magnetises the copper, and because of the magnetic field it creates, which in turn opposes the falling of the magnet. This is an electrical effect, not a permanent magnetic attraction.

How can I tell if my copper is pure?

Pure copper is reddish and non-magnetic. The melting point of copper is 1,085°C. If it sticks to a magnet, it is copper-plated onto steel or heavily contaminated with iron.

Can cold-working make copper magnetic?

No. Cold-working can increase hardness, alter the grain structure, and make a material more ferromagnetic, but in the case of copper, cold-working does not alter the electronic structure of the material.

Is brass magnetic?

Std. Brass is an alloy of copper and zinc. It is not magnetic. If you find that some Brass items are magnetic, it is most likely that they have a steel core or are magnetized and perhaps made of a nickel-iron alloy of some type.

References

1. Lide, D. R. (2023). CRC Handbook of Chemistry and Physics.
2. Copper Development Association (CDA). (2024). Electrical Properties of Copper and Copper Alloys.
3. Griffiths, D. J. (2022). Introduction to Electrodynamics.
4. ASTM B193 – 20. Standard Test Method for Resistivity of Electrical Conductor Materials.
5. Kittel, C. (2021). Introduction to Solid State Physics.