Copper is not magnetic in the way most people understand the term. A standard permanent magnet will not attract a piece of pure copper metal. This lack of attraction is a consequence of copper’s atomic structure, which places it in a category of materials that exhibit a very slight repulsion to magnetic fields, a property known as diamagnetism. Understanding this behavior requires a deeper look into how different materials interact with an external magnetic field.
Defining the Types of Magnetism
Materials are classified into three categories based on their response to a magnetic field. The most familiar category is ferromagnetism, which describes materials like iron, cobalt, and nickel that are strongly attracted to magnets and can retain their own magnetization after the external field is removed. This attraction is due to the presence of uncompensated electron spins within the material, which align themselves into large regions called magnetic domains. When exposed to an external field, these domains align, creating a powerful net magnetic force.
Paramagnetism is a weaker form of attraction found in materials that contain unpaired electrons, but these electrons do not align into permanent domains. When an external magnetic field is applied, these electrons align weakly with the field, resulting in a slight attraction. This induced magnetism is temporary and disappears as soon as the external field is withdrawn. Aluminum is a common example of a paramagnetic material.
Diamagnetism represents the third class, characterized by a weak repulsion from a magnetic field. This effect is present in all materials, but it is masked by stronger ferromagnetism or paramagnetism. Diamagnetism arises from the orbital motion of electrons, which is slightly altered by the external field to induce a magnetic moment that opposes the field, according to Lenz’s Law. Materials classified as purely diamagnetic, such as copper, have all of their electrons paired, meaning they lack the unpaired electrons necessary for stronger magnetic effects.
Copper’s Atomic Structure and Magnetic Classification
The magnetic classification of bulk copper is in the diamagnetic category, which is directly linked to its electron configuration. Copper has an atomic number of 29. In its metallic form, the electrons are arranged such that all the electrons in the inner shells, including the \(3d\) subshell, are paired. The electron configuration for an isolated copper atom is \([Ar] 3d^{10} 4s^1\), showing one electron in the outermost \(4s\) orbital.
In bulk metallic copper, this single \(4s\) electron becomes delocalized, forming the “sea” of electrons responsible for its high electrical conductivity. The magnetic behavior is dominated by the filled \(3d^{10}\) subshell, where all electrons are paired with opposite spins. Paired electrons cancel out their magnetic moments, leaving no net permanent magnetic moment on the atom.
Because copper lacks the unpaired electrons and magnetic domains necessary for attraction, the diamagnetic effect prevails. A piece of pure copper will exhibit a negative magnetic susceptibility, confirming its classification as a weakly field-repelling material. While trace impurities in commercial copper can sometimes introduce a slight paramagnetic component, the intrinsic behavior of the pure metal remains diamagnetic.
How Copper Interacts with Magnetic Fields
Despite being non-magnetic in the traditional sense, copper interacts significantly with moving or changing magnetic fields. This interaction is not a function of its diamagnetism but a direct result of its high electrical conductivity. Copper is second only to silver in its ability to conduct electricity, a property that makes it highly susceptible to electromagnetic induction.
When a magnet is moved near a piece of copper, the changing magnetic flux induces circulating electrical currents within the metal known as eddy currents. These currents generate their own magnetic field that opposes the original change in flux, in accordance with Lenz’s Law. This opposition causes magnetic braking, where a magnet falling through a copper pipe slows significantly as if it were falling through a viscous fluid.
This principle is harnessed in various technological applications, such as braking systems in high-speed trains and metal detectors. Copper’s role in magnetic technology is not as a magnetic material itself, but as a conductor that translates a changing magnetic field into an opposing force. This allows copper to be used extensively in electromagnets as the wire coil to create the magnetic field.