Not all metals are magnetic. Magnetism is a physical property dependent on the arrangement of electrons within a material’s atomic structure.
The Atomic Basis of Magnetism
Magnetism originates from the behavior of electrons within atoms. Each electron possesses an intrinsic “spin,” generating a tiny magnetic field.
In most atoms, electrons occupy orbitals in pairs, with opposing spins that cancel out their magnetic fields, resulting in no net magnetic moment. However, some atoms possess unpaired electrons, giving the atom a net magnetic moment. In certain materials, these atomic magnetic moments can align within small regions called magnetic domains, which are crucial for strong magnetism.
How Different Materials Interact with Magnetic Fields
Materials interact with magnetic fields in distinct ways, categorized into three types based on their electron configurations. Ferromagnetic materials are strongly attracted to magnets and can become permanently magnetized. This occurs because their atomic magnetic moments, arising from unpaired electrons, spontaneously align within magnetic domains, which then align with an external magnetic field. Iron, nickel, and cobalt are common elemental examples of ferromagnetic metals, useful in many applications due to their strong magnetic response.
Paramagnetic materials exhibit a weak attraction to strong magnetic fields but do not retain magnetism once the external field is removed. These materials also have unpaired electrons, but their atomic magnetic moments are randomly oriented and only temporarily align with an applied magnetic field. Examples of paramagnetic metals include aluminum and platinum.
Diamagnetic materials are weakly repelled by magnetic fields. Unlike ferromagnetic or paramagnetic substances, all electrons in diamagnetic materials are paired, meaning they have no permanent atomic magnetic moments. When an external magnetic field is applied, it induces a very slight opposing magnetic field within the material, causing the weak repulsion. Common diamagnetic metals include copper, gold, silver, and bismuth.
Common Examples of Magnetic and Non-Magnetic Metals
Ferromagnetic metals are what people typically associate with “magnetic” properties, as they are easily attracted to a magnet and can become magnetized. Many other common metals, such as aluminum, copper, gold, and silver, are non-magnetic, being either paramagnetic or diamagnetic.
Alloys, which are mixtures of metals, can also vary in their magnetic properties. For instance, while steel is primarily iron and often magnetic, certain types of stainless steel are non-magnetic. This is because the addition of elements like chromium and nickel can alter the metal’s internal structure, making it non-magnetic despite its iron content.
Beyond Basic Properties: Factors Affecting Magnetism
Factors beyond a metal’s atomic structure influence its magnetic behavior. Temperature plays a significant role for ferromagnetic materials. Each ferromagnetic substance has a specific temperature, the Curie point, above which it loses its strong magnetic properties and becomes paramagnetic. For example, iron loses ferromagnetism above approximately 770°C, while nickel’s Curie point is around 358°C.
External magnetic fields can also alter a metal’s magnetic state. A strong external field can induce temporary magnetism in some materials or demagnetize others. The composition of alloys and the presence of impurities significantly impact magnetic properties, as specific alloying elements can prevent the formation of magnetic domains. Heat treatments can also change the microstructure of an alloy, influencing its magnetic response.