Magnets produce a force field that creates attraction with certain materials, but this interaction is highly selective. Although many people assume all metals are magnetic, the ability to stick to a magnet is a special property reserved for only a small group of metals. This strong, noticeable attraction is a result of ferromagnetism, meaning only a few elemental metals and their specific alloys can respond to a magnet’s pull.
The Ferromagnetic Metals
Only three elements exhibit strong ferromagnetism at room temperature: iron (Fe), nickel (Ni), and cobalt (Co). These metals possess a crystalline structure that allows their atomic magnetic forces to align powerfully, resulting in the familiar magnetic pull.
Iron is the most common example, forming the basis of many everyday magnetic objects. The magnetic properties extend to alloys, which are mixtures of these metals. For instance, steel, an alloy of iron and carbon, is the most frequently encountered magnetic material in daily life.
The magnetic responsiveness of an alloy depends on the presence and proportion of a ferromagnetic element in its composition. Stainless steel, a common alloy, may or may not be magnetic. If stainless steel contains a high percentage of nickel and chromium, it can alter the crystalline structure and reduce the magnetic attraction.
The Atomic Reason for Attraction
The ability of iron, nickel, and cobalt to stick to a magnet originates at the atomic level with the behavior of electrons. Every electron behaves like a tiny, spinning magnet, a property known as electron spin. In most atoms, electrons exist in pairs with opposite spins, which cancels out their individual magnetic effects.
Ferromagnetic materials are unique because their atoms contain unpaired electrons whose spins are aligned in the same direction. This alignment causes each atom to possess a net magnetic moment, making the atom a microscopic magnet. Within the bulk material, these atomic magnets spontaneously group into small regions called magnetic domains.
In an unmagnetized piece of iron, these domains are oriented randomly, meaning their overall magnetic fields cancel each other out. When a magnet is brought near, its external magnetic field causes the domain boundaries to shift. The domains aligned with the external field grow larger, and the others rotate to align with it. This collective alignment creates a strong internal magnetic field that results in the visible attraction to the magnet.
Why Most Metals Are Not Magnetic
While all metals are affected by magnetic fields to some degree, most do not stick to a magnet because they are not ferromagnetic. Familiar metals like aluminum, copper, silver, and gold fall into two other classifications: paramagnetic or diamagnetic. These metals do not possess the necessary unpaired electron structure or the long-range atomic order required to form magnetic domains.
Paramagnetic metals, such as aluminum and platinum, have a weak attraction to a magnet. Their unpaired electrons align with an external magnetic field, but this alignment is temporary and disappears when the magnet is removed. The resulting attraction is so slight that it is not noticeable outside of laboratory conditions.
Diamagnetic metals, including copper, gold, and silver, exhibit the opposite behavior. These materials are weakly repelled by a magnetic field. This slight repulsion is caused by the magnetic field inducing a change in the orbit of their paired electrons, creating a magnetic field in the opposite direction.