Gold (Au) is a noble metal renowned for its brilliant luster, resistance to corrosion, and malleability. While it shares the metallic classification with materials like iron and nickel, its physical properties are distinct, particularly concerning its magnetic response. Pure gold does not attract or stick to a common magnet, placing it firmly in the category of nonmagnetic materials. Its interaction with a magnetic field is specifically categorized as diamagnetism.
The Simple Answer: Diamagnetism
Diamagnetism describes a material’s very weak repulsion when placed in an external magnetic field. This force is exceedingly subtle and generally requires specialized, high-field laboratory equipment to detect. Pure gold is considered diamagnetic, meaning it creates a slight induced magnetic field that momentarily opposes the external field.
This weak repulsion is why gold is commonly referred to as “nonmagnetic” in everyday conversation. The effect is so slight that gold jewelry will not visibly react to a magnet, making the material practically inert to magnetic forces under ordinary conditions.
Understanding Magnetic Categories
Materials are classified into three primary categories based on how their atoms respond to an external magnetic field. Ferromagnetism, which includes iron, nickel, and cobalt, involves a strong, lasting attraction because internal magnetic moments align spontaneously. These materials can be permanently magnetized.
Paramagnetic materials, such as aluminum and platinum, exhibit a much weaker attraction that disappears when the external field is removed. This weak attraction occurs because their atoms possess small, temporary magnetic moments that align briefly with the applied field. Diamagnetism is the third class, where materials like gold, copper, and water are weakly repelled, creating an induced field opposite to the external one.
Why Pure Gold Resists Magnetic Fields
The magnetic behavior of any element is determined by the configuration of its electrons within their atomic orbitals. Pure bulk gold is diamagnetic because all of its electrons are effectively paired, meaning their opposing spins cancel out any inherent magnetic moment. Since there is no net intrinsic atomic magnetism, the material cannot align itself with an external field to create attraction.
When an external magnetic field is applied to gold, it slightly distorts the orbits of these paired electrons. This orbital distortion induces a small, temporary current within the material, a phenomenon described by Lenz’s Law. The induced current generates its own extremely weak magnetic field, which is always directed opposite to the external field. This counteracting force is the physical mechanism behind the material’s slight repulsion.
When Gold Appears Magnetic
The most common scenario where gold appears magnetic is when it is not in its pure, 24-karat form. Gold used in jewelry and coinage is routinely mixed with other metals to increase hardness and durability, forming an alloy. If the gold is alloyed with ferromagnetic metals such as iron, nickel, or cobalt, the resulting material will exhibit a magnetic attraction.
White gold, for example, often contains nickel, and its magnetic response is entirely due to the proportion of this strongly magnetic additive metal, not the gold itself. Even small amounts of ferromagnetic impurities or trace iron contamination from manufacturing processes can cause a slight magnetic pull in an otherwise nonmagnetic gold item.