Magnetism is a fundamental force describing the attraction or repulsion of materials, originating from the motion of electrons within atoms. While many people assume metals are magnetic, the vast majority do not display the familiar attraction associated with a refrigerator magnet. Non-magnetic metals exhibit unique, subtle interactions with a magnetic field, depending entirely on the material’s atomic structure.
The Three Categories of Magnetic Interaction
A material’s magnetic nature is determined by how it responds to an external magnetic field, which places it into one of three primary categories. The most recognizable group is ferromagnetism, which includes iron, nickel, and cobalt, the so-called “magnetic trio.” These materials contain unpaired electrons that align their magnetic moments into small regions called domains, which remain aligned even after the external field is removed, leading to a strong, permanent attraction.
Paramagnetic materials are weakly attracted to a magnetic field, but they lose this magnetism instantly when the field is taken away. This weak attraction is caused by atoms that possess some unpaired electrons. These electrons create tiny, randomly oriented internal magnetic moments that temporarily align in the presence of an external field.
Diamagnetic materials exhibit the weakest interaction of all, showing a slight repulsion when exposed to a magnetic field. Diamagnetism arises from the orbital motion of paired electrons. The application of an external field induces a small magnetic moment that opposes the applied field. This effect is only noticeable when stronger magnetic effects are absent.
Non-Magnetic Metals: Diamagnetic and Paramagnetic Examples
Copper is a diamagnetic metal, meaning it is very weakly repelled by a magnet. Widely used in electrical wiring, its excellent conductivity makes its diamagnetic property a secondary consideration.
Other precious metals also exhibit this slight repulsion, including pure gold and silver. Gold’s non-magnetic nature makes it suitable for sensitive electronic components where magnetic interference must be avoided. Zinc is another common diamagnetic metal, often used as a protective coating on steel through galvanization.
Aluminum is the most well-known example of a paramagnetic metal, displaying a minute attraction to a magnetic field. Its light weight and resistance to corrosion make it a primary material for aircraft and beverage cans. Platinum is another paramagnetic metal, often employed in laboratory equipment, and its weak attraction is due to its atomic structure having unpaired electrons.
How Alloys and Temperature Change Magnetic Properties
The magnetic classification of a pure metal can change entirely when it is mixed with other elements to form an alloy. Stainless steel, a common alloy of iron, chromium, and often nickel, exemplifies this complexity. Whether stainless steel is magnetic depends on its specific crystal structure, determined by the alloying elements and processing.
Austenitic stainless steels are typically non-magnetic because the addition of nickel stabilizes a crystal structure that prevents the alignment of magnetic domains. Conversely, ferritic and martensitic stainless steels retain their magnetic properties because they possess a different structure that allows for ferromagnetic behavior. Cold working can also alter the crystal structure of non-magnetic austenitic steel, causing it to become weakly magnetic in certain areas.
Temperature provides another means to fundamentally alter a metal’s magnetic state. Ferromagnetic materials possess a Curie Point. When heated above this temperature, the intense thermal energy overcomes the internal forces that keep the magnetic domains aligned. The material instantly loses its strong, permanent magnetism and transitions into a paramagnetic state. This change is reversible; once the metal cools below its Curie Point, it regains its ferromagnetic properties.