Magnetism is a fundamental force that causes objects to attract or repel each other through a magnetic field. While all substances exhibit some magnetism, only a few materials are considered “magnetic” in the everyday sense, showing a strong attraction to a magnet. Understanding which metals possess this strong magnetic property involves exploring their atomic structures and how they respond to magnetic fields.
Understanding How Magnetism Works
Magnetism originates at the atomic level, primarily with electron behavior. Each electron behaves like a tiny magnet due to its “spin,” generating a small magnetic field. In most materials, electrons exist in pairs with opposite spins, canceling their individual magnetic fields. Consequently, these materials do not exhibit a net magnetic effect.
However, in certain atoms, some electrons remain unpaired. These unpaired electrons contribute to a net magnetic moment, making each atom a tiny dipole, similar to a miniature bar magnet.
Within magnetic materials, these atomic magnets do not act independently. Instead, groups of atoms spontaneously align their magnetic moments, forming microscopic regions called magnetic domains. In an unmagnetized material, these domains are randomly oriented, and their magnetic fields largely cancel, resulting in no overall magnetism. When an external magnetic field is applied, these domains can rotate and align with the external field. Their behavior and interaction determine the material’s overall magnetic properties.
The Truly Magnetic Metals: Ferromagnets
The metals considered “truly magnetic” are known as ferromagnetic materials. These materials exhibit a strong attraction to magnetic fields and can retain magnetism after the external field is removed, becoming permanent magnets. This distinct behavior arises from strong atomic interactions that cause their magnetic domains to spontaneously align in parallel, even without an external field.
The primary elemental metals ferromagnetic at room temperature are iron (Fe), nickel (Ni), and cobalt (Co). Gadolinium (Gd) is another ferromagnetic element, though its properties are typically observed below room temperature, around 20 degrees Celsius. These elements possess particular electronic configurations favoring the alignment of unpaired electron spins, leading to strong magnetic properties.
Beyond these elements, many alloys also exhibit ferromagnetism. Steel, an alloy primarily of iron and carbon, is a common example. Other notable ferromagnetic alloys include alnico, which contains iron, nickel, cobalt, and aluminum, and is used for strong permanent magnets. Neodymium magnets, known for their powerful magnetic strength, are alloys of neodymium, iron, and boron.
Metals with Weaker Magnetic Responses
While ferromagnets are strongly attracted to magnets, all materials interact with magnetic fields to some extent. This range includes paramagnetism and diamagnetism.
Paramagnetic materials are weakly attracted to an external magnetic field. This occurs because they have some unpaired electrons whose magnetic moments align with the applied field, but this alignment is temporary and disappears when the field is removed. Examples of paramagnetic metals include aluminum, platinum, magnesium, molybdenum, lithium, and tungsten. Liquid oxygen also demonstrates paramagnetism.
In contrast, diamagnetic materials are weakly repelled by magnetic fields. This behavior arises because all electrons are paired, meaning they have no permanent magnetic moments. When an external magnetic field is applied, it induces a very weak magnetic field in the material that opposes the external field, leading to slight repulsion. Most elements in the periodic table, including metals like copper, gold, silver, bismuth, and zinc, are diamagnetic. Water is another common diamagnetic substance. The magnetic forces in paramagnetic and diamagnetic materials are too weak to be felt without specialized laboratory equipment.
What Influences a Metal’s Magnetism
A metal’s magnetic properties can be influenced by several factors. Temperature plays a significant role; for ferromagnetic materials, there is a specific temperature known as the Curie point. Above this temperature, thermal energy disrupts the alignment of magnetic domains, causing the material to lose its strong ferromagnetic properties and become paramagnetic. For example, iron has a Curie point of approximately 770 °C (1,418 °F), while nickel’s is about 354 °C (669 °F) and cobalt’s is around 1,130 °C (2,066 °F).
The addition of other elements, known as alloying, can also significantly alter a metal’s magnetism. For instance, adding non-magnetic elements like chromium and nickel to iron can reduce or even eliminate the ferromagnetic properties of steel, as seen in some stainless steels. Conversely, specific alloying elements can enhance or create magnetic properties in materials not originally ferromagnetic. For example, silicon added to steel can reduce magnetic saturation and lower the Curie temperature.
External magnetic fields can also influence a metal’s magnetism. Applying an external magnetic field can induce magnetism by aligning its magnetic domains. The material’s microstructure, including crystal structure and grain size, also affects how easily domains align and influences its magnetic response. Mechanical stress or deformation can also impact magnetic properties by altering internal structure and domain orientation.