Nonmagnetic materials are substances that do not exhibit a noticeable attraction to a standard magnet in everyday settings. While they are not entirely without magnetic properties, their fundamental atomic structure prevents them from displaying the strong, permanent magnetism seen in materials like iron. The behavior of these materials is rooted in the subatomic world, specifically in how their electrons are arranged.
The Atomic Basis of Magnetism
The source of all magnetism lies within the atom, specifically with the electrons. Electrons are charged particles that are constantly in motion, both orbiting the nucleus and possessing an intrinsic property known as spin. Any moving electrical charge generates a magnetic field, meaning every electron acts like a tiny, elementary magnet with its own magnetic moment. The overall magnetic behavior of a material is determined by the combined effect of these individual atomic magnetic moments.
In most materials, the magnetic effects from these electrons cancel each other out. This cancellation occurs because electrons often exist in pairs within an atom, with each electron spinning in an opposite direction. The magnetic field generated by one electron’s spin is perfectly opposed and neutralized by its partner’s opposite spin. A net magnetic moment for an atom only arises when there are unpaired electrons whose individual magnetic fields are unopposed.
Defining Nonmagnetic Behavior
Materials commonly labeled as nonmagnetic fall into two distinct scientific categories based on how their electrons are arranged: diamagnetic and paramagnetic. These classifications describe a substance’s weak response to an external magnetic field. Neither category displays the strong, spontaneous attraction seen in ferromagnetic materials like iron, nickel, or cobalt.
Diamagnetism occurs in materials where all electrons are paired, leading to a zero net magnetic moment for each atom in the absence of an external field. When an external magnetic field is applied, it induces a temporary, opposing magnetic field within the material, causing a slight repulsion. This effect is a universal property of all matter, but it is typically masked by stronger magnetic responses in other substances.
Paramagnetism arises in substances that possess atoms with one or more unpaired electrons, giving each atom a permanent magnetic moment. However, these tiny internal magnets are randomly oriented due to thermal energy when no external field is present, resulting in zero overall magnetism. Applying an external magnetic field causes these atomic moments to temporarily align with the field, leading to a weak attraction.
Common Diamagnetic Materials
Diamagnetic materials are weakly repelled by a magnetic field. Water is a common example of a diamagnetic substance, a property that is visually demonstrated when a droplet is repelled by a very strong magnet. Many familiar non-metallic substances, such as wood, plastic, and glass, also exhibit this characteristic.
Certain metals, including copper, silver, and gold, are also classified as diamagnetic, as are the noble gases like helium and neon. The element bismuth is notable for being the most strongly diamagnetic of all non-superconducting elements, displaying the most pronounced repulsion. This strong diamagnetic effect is occasionally used in laboratory demonstrations to achieve magnetic levitation of small objects.
Common Paramagnetic Materials
Paramagnetic materials contain unpaired electrons, which gives them a slight, temporary attraction to an external magnetic field. Despite this attraction, the force is so weak that these substances are considered nonmagnetic in practical, everyday situations. Aluminum is a well-known example; while it is attracted to a strong magnet, the force is negligible compared to the attraction of iron.
Other common elements that exhibit this behavior include magnesium and titanium, both of which have unpaired electrons in their atomic structure. Even liquid oxygen, a substance that is not a metal, is paramagnetic, a property that can be demonstrated by seeing it weakly suspended between the poles of a powerful magnet. This weak, positive attraction is only maintained while the external magnetic field is actively applied, as the thermal energy of the material quickly randomizes the electron spins once the field is removed.