Paper clips are a ubiquitous item in offices and homes, often used without much thought about their composition or properties. A common observation is their tendency to cling to magnets, which raises a question about their inherent magnetic nature. Understanding this phenomenon involves exploring the material science behind paper clips and the principles of magnetism.
What Paper Clips Are Made From
Most paper clips are typically manufactured from steel wire. Steel itself is an alloy, meaning it is a mixture of metals, primarily composed of iron. This iron content is particularly important because iron is classified as a ferromagnetic material. While some paper clips may be covered in plastic or have a galvanized coating for rust resistance, their core is still predominantly steel. The presence of iron in their composition forms the basis for their interaction with magnets.
Why Paper Clips Stick to Magnets
Paper clips are not inherently magnetic on their own, meaning they do not produce their own magnetic field. Instead, they become magnetic through induced magnetism when placed near a permanent magnet. When a paper clip, made of ferromagnetic steel, comes close to a magnet, the magnet’s external magnetic field influences its internal structure, causing its tiny magnetic regions, called magnetic domains, to align. Normally, these domains are randomly oriented, canceling out any overall magnetic effect. However, under the influence of the external magnet, these domains temporarily align, making the paper clip act like a temporary magnet and creating an attractive force.
How Materials Become Magnetic
Materials exhibit different responses to magnetic fields, categorized into three types: ferromagnetic, paramagnetic, and diamagnetic. Ferromagnetic materials, like iron, nickel, and cobalt, show a strong attraction to magnets because their atomic magnetic moments spontaneously align in regions called domains when an external field is applied, leading to strong magnetization. Paramagnetic materials, such as aluminum, have unpaired electrons that create small magnetic moments. These moments align weakly with an external magnetic field, resulting in a slight attraction, but they lose this magnetism once the field is removed. In contrast, diamagnetic materials, like copper or water, have all paired electrons and develop a very weak magnetic moment that opposes the applied field, causing a slight repulsion.
Making a Paper Clip a Temporary Magnet
A paper clip can be transformed into a temporary magnet through a simple physical action. By repeatedly stroking a paper clip in one direction with a permanent magnet, one can observe this effect. This action helps to coax the magnetic domains within the paper clip’s steel to align in a more uniform direction. Each stroke contributes to a greater alignment of these internal magnetic regions, building up the paper clip’s temporary magnetic properties. Once a sufficient number of domains are aligned, the paper clip will be able to attract other small ferromagnetic objects, like another paper clip. This magnetic effect is not permanent, however, because the aligned domains will gradually return to their random orientations over time or if the paper clip is jarred. The paper clip then loses its induced magnetism.