Cobalt is a fundamental and extensively used component in high-performance magnets, while gold is not. Cobalt is one of only three naturally occurring elements that exhibit ferromagnetism, the property that allows a material to form a permanent magnet. Gold is classified as diamagnetic, meaning it is slightly repelled by a magnetic field and cannot be used to create a conventional magnet. This distinction arises from the atomic structure of each element and dictates their vastly different roles in modern technology.
Fundamental Magnetic Behavior of Cobalt Versus Gold
The ability of a material to become a strong, permanent magnet is determined by the behavior of its electrons at the atomic level. Cobalt is ferromagnetic because its atoms possess unpaired electrons in the 3d orbital. These unpaired electrons act like tiny magnets, creating a net magnetic moment for the atom. In bulk cobalt, these moments spontaneously align within microscopic regions called magnetic domains. When an external field is applied, these domains align, and a significant portion of that alignment remains after the field is removed, resulting in a permanent magnet.
Cobalt’s ferromagnetism is enhanced by its high Curie temperature of approximately 1,115°C, the point above which a material loses its permanent magnetism. This high thermal stability means cobalt magnets can operate reliably in high-heat environments where other magnetic materials would fail.
Gold, conversely, is a diamagnetic material because all of its electrons are paired. In a diamagnetic atom, the magnetic moments of the electrons cancel each other out, resulting in no net magnetic moment. When an external magnetic field is applied, it induces a very weak magnetic moment in the opposite direction.
Consequently, pure gold is slightly repelled by a magnetic field and cannot retain any magnetization, making it unsuitable for manufacturing permanent magnets. The core difference is that cobalt’s unpaired electrons allow for the sustained, cooperative alignment necessary for ferromagnetism, while gold’s fully paired electrons prohibit this strong magnetic response.
Essential Role of Cobalt in High-Performance Magnetic Alloys
Cobalt’s magnetic properties are crucial in the composition of high-performance magnetic alloys, not just in its pure form. It is a defining component in Samarium Cobalt (SmCo) magnets, a class of powerful rare-earth magnets. SmCo magnets, typically composed of SmCo\(_{5}\) or Sm\(_{2}\)Co\(_{17}\), contain a high percentage of cobalt, often around 65%. They are valued for their exceptional thermal stability and strong resistance to demagnetization, making them essential for applications in aerospace and high-performance motors.
Cobalt also plays a targeted role in Neodymium-Iron-Boron (NdFeB) magnets, the world’s strongest permanent magnets. NdFeB magnets primarily contain iron and neodymium, but they incorporate a small amount of cobalt, typically around 1.5% by weight. This addition improves both their corrosion resistance and their thermal stability by raising the Curie temperature of the alloy.
This is particularly important for magnets used in electric vehicle traction motors and wind turbine generators, where temperatures can exceed 150°C. Cobalt helps maintain the magnet’s coercivity, or resistance to demagnetization, under these demanding thermal conditions. Older magnetic alloys, such as Alnico (Aluminum-Nickel-Cobalt), also rely on cobalt to achieve magnetic strength and stability for various industrial uses.
Gold’s Use in Electronics and Magnetic System Components
While gold is not a magnetic material, it is used extensively in electronic systems that rely on magnets. Gold’s primary value in electronics stems from its superior electrical conductivity and its resistance to corrosion and tarnish. This combination ensures reliable, long-term electrical connections.
The metal is commonly applied as a thin plating on connectors, switch contacts, and printed circuit boards. Its resistance to oxidation guarantees a low-resistance current path. Gold plating is often found in devices like hard disk drives and sophisticated sensors that depend on high-performance magnets.
In these systems, gold’s role is purely conductive and protective, safeguarding the electronic signals that communicate with the magnetic components. For instance, hard drive read/write heads rely on gold-plated contacts to transmit data reliably. Gold’s exceptional durability and conductivity are the reasons for its use, not any inherent magnetic property.
In its common industrial applications, gold functions as a conductor and protective layer, serving a purpose entirely separate from the generation of a magnetic field.