A standard paper clip does not possess its own permanent magnetic field, but it is highly susceptible to becoming a magnet itself when placed near a powerful external magnet. This temporary magnetic state is a direct result of the atomic structure of the metal used in its construction. Understanding this process requires exploring the specific material science and the magnetic processes that allow this common office supply to briefly exhibit magnetic properties.
The Material Composition of Paper Clips
Most metal paper clips found in offices are manufactured from steel wire, an alloy composed primarily of iron and a small amount of carbon. Iron, along with a few other elements like nickel and cobalt, belongs to a special class of materials that are strongly attracted to magnets. To prevent rust and corrosion, the steel wire is often treated, typically by being electrogalvanized with zinc or plated with nickel. This thin protective coating does not interfere with the underlying metal’s ability to respond to a magnetic field.
Understanding Ferromagnetism and Magnetic Domains
The strong reaction of iron-containing materials to magnets is due to ferromagnetism, the strongest type of magnetism. This phenomenon is characterized by the alignment of atomic magnetic moments within the material. These moments are essentially tiny magnetic fields created by the motion of electrons within the atoms.
Within a ferromagnetic substance, groups of atoms spontaneously align their moments to form small, distinct regions known as magnetic domains. In a paper clip not near a magnet, these domains are oriented randomly, causing their individual magnetic fields to cancel out. When an external magnet is brought close, its magnetic field penetrates the paper clip and influences the internal domains. The domains aligned with the external field begin to grow or rotate to match the applied field’s direction. This coordinated alignment creates a net magnetic field, effectively turning the paper clip into a temporary magnet.
How Paper Clips Gain and Lose Temporary Magnetism
The process by which a paper clip temporarily becomes magnetized is called magnetic induction. When the external magnet is held near the paper clip, the clip’s domains align, and the end closest to the magnet develops an opposite magnetic pole. This induced opposite pole is strongly attracted to the magnet, which is why the paper clip snaps onto it.
This temporary magnetism allows for a common demonstration where a chain of paper clips can hang from a single permanent magnet. The first paper clip is induced into a magnet by the permanent magnet, and it then induces the next paper clip into a magnet, creating a chain reaction. Each clip in the chain is only magnetic as long as it remains within the magnetic influence of the clip before it.
Paper clips are categorized as “soft” magnetic materials. This means they are easy to magnetize but also lose their magnetism quickly when the external field is removed. Once the permanent magnet is pulled away, the domains within the paper clip’s steel quickly return to their random, unaligned state. This rapid loss of alignment is due to the material having low coercivity, meaning it requires very little energy to demagnetize. In contrast, “hard” magnetic materials, used to make permanent magnets, have high coercivity and retain a significant amount of residual magnetism after the external field is gone.