Magnetism is a fundamental force, allowing objects to attract or repel each other through a magnetic field. This field arises from the movement of electric charges, often the electrons within a material’s atoms. The question of whether any metal can be magnetized is complex, as different metals interact with magnetic fields in distinct ways. Understanding these interactions reveals why some metals become strong magnets while others exhibit only very weak magnetic behavior.
Metals That Can Be Magnetized
Only a select group of metals can be strongly magnetized and retain their magnetic properties, forming permanent magnets. These include iron, nickel, cobalt, and many of their alloys like steel. This strong magnetic behavior is called ferromagnetism, a term derived from “ferrum,” the Latin word for iron.
The ability of these materials to become strongly magnetized stems from their atomic structure. Within ferromagnetic metals, electron spins align parallel, creating tiny, spontaneously magnetized regions called magnetic domains. In an unmagnetized state, these domains are oriented randomly, cancelling out their individual magnetic effects.
When an external magnetic field is applied, these magnetic domains align with the field’s direction. If the field is sufficiently strong, this alignment can become fixed even after the external field is removed. This permanent alignment allows the material to generate its own persistent magnetic field. Alloys like Alnico (aluminum, nickel, cobalt, iron) and Neodymium-Iron-Boron (NdFeB) are examples engineered for robust ferromagnetic properties.
Metals With Weak Magnetic Behavior
Beyond ferromagnetic materials, other metals exhibit much weaker magnetic interactions. These are categorized into paramagnetic and diamagnetic materials, neither of which can be made into permanent magnets. Their magnetic responses are temporary and only observable in an external magnetic field.
Paramagnetic materials, such as aluminum, platinum, magnesium, and titanium, are weakly attracted to a strong magnetic field. This attraction occurs because these metals contain unpaired electrons, whose spins can partially align with an external magnetic field. However, this alignment is temporary; once the external field is removed, thermal motion randomizes the electron spins, and the material loses its weak magnetism.
In contrast, diamagnetic materials like copper, gold, silver, and bismuth are weakly repelled by magnetic fields. All materials exhibit diamagnetism to some extent, but it is often overshadowed by stronger magnetic properties if they are present. Diamagnetism arises because all electrons in these materials are paired, meaning their magnetic moments cancel out. When an external magnetic field is applied, it induces a weak magnetic field within the material that opposes the applied field, resulting in a slight repulsive force.
Factors Influencing Magnetization
Several factors influence a metal’s ability to be magnetized or the strength of its magnetism. Temperature plays a significant role, as higher temperatures weaken a magnet’s strength. As a material heats, increased kinetic energy causes atoms and their magnetic domains to move more vigorously and become misaligned.
A specific temperature, known as the Curie temperature or Curie point, marks a threshold. Above this temperature, ferromagnetic materials completely lose their strong magnetic properties and become paramagnetic. For example, iron has a Curie temperature of approximately 770°C. While cooling below the Curie point can restore ferromagnetism, heating beyond this point can lead to irreversible magnetism loss.
The strength of the external magnetic field applied during magnetization dictates the resulting magnetic strength. A stronger applied field can align more magnetic domains within a ferromagnetic material, leading to a more potent permanent magnet. Conversely, a strong opposing magnetic field can demagnetize a material.
Material composition and purity affect magnetic properties. Alloying ferromagnetic metals with other elements can significantly alter their magnetic characteristics, sometimes enhancing them to create stronger magnets or tailoring them for specific applications.
Physical stress or impact, such as dropping or hammering a magnet, can disrupt magnetic domain alignment, potentially causing a magnet to lose strength or become demagnetized.