When holding a common coin and a household magnet, a natural question arises: will the coin stick? The interaction between a coin and a magnet depends entirely on its fundamental composition. Exploring this phenomenon reveals interesting aspects of material science and currency production.
Understanding Magnetism
Magnetism is a fundamental force arising from the behavior of electrons within materials. When atomic magnetic moments align, the material exhibits magnetic properties. Materials are classified into three main types based on their response to a magnetic field: ferromagnetic, paramagnetic, and diamagnetic.
Ferromagnetic materials, such as iron, nickel, and cobalt, show a strong attraction to magnets. Their atomic magnetic moments can align spontaneously, creating internal magnetic regions called domains. These domains are easily oriented by an external magnetic field, resulting in a noticeable pull.
Paramagnetic materials, like aluminum, have unpaired electrons that create weak magnetic moments, leading to a slight attraction. Diamagnetic materials, including copper and silver, have all their electrons paired, causing a slight repulsion when exposed to a magnetic field, an effect typically too weak to observe with common magnets.
Why Most Circulation Coins Aren’t Magnetic
The majority of modern coins in everyday circulation do not stick to a magnet. This is primarily because they are made from metal compositions that are not ferromagnetic. For instance, most United States coinage utilizes largely non-magnetic alloys. US pennies are primarily copper-plated zinc, while dimes and quarters are copper-nickel alloys. Even the US five-cent coin, commonly called a “nickel,” is 75% copper and only 25% nickel, which is insufficient for a strong magnetic response.
These widely used alloys, such as copper, zinc, and cupronickel, are typically paramagnetic or diamagnetic. While they may interact with a strong magnetic field at a microscopic level, they do not exhibit the strong attraction a common magnet can detect. Mints often choose these non-ferromagnetic materials for durability, appearance, and cost-effectiveness.
Coins That Attract a Magnet
Despite most coins being non-magnetic, some circulation coins do attract a magnet due to their specific metal content. The magnetic property comes from the inclusion of ferromagnetic metals like steel or pure nickel. Such coins are often produced for economic reasons, as steel can be a cheaper alternative to other metals.
A notable example in the United States is the 1943 steel penny, minted during World War II to conserve copper. These pennies are made of steel coated with zinc and are readily magnetic. In the United Kingdom, 1 pence and 2 pence coins (since 1992) and 5 pence and 10 pence coins (since 2012) are copper-plated or nickel-plated steel, making them magnetic. Many Canadian coins minted after 2000 also incorporate steel or a significant amount of nickel in their composition, which makes them magnetic.