Magnetic metals are scientifically categorized as ferromagnetic substances, a term derived from ferrum, the Latin word for iron. Ferromagnetic materials exhibit the strongest and most recognizable form of magnetism, enabling them to be formed into permanent magnets or to be powerfully attracted to them. Their ability to retain a magnetic field after the external source is removed distinguishes them from nearly all other types of matter.
The Core Answer: Ferromagnetic Materials
Ferromagnetism is the property that allows certain materials to exhibit spontaneous magnetization, meaning they possess a net magnetic field even without an external one. This characteristic arises from the unique atomic structure of these materials, which enables a strong, cooperative alignment of magnetic moments across many atoms. The most commonly recognized elements that display ferromagnetism at room temperature are iron, nickel, and cobalt. While these pure elements are ferromagnetic, many of the most powerful magnets are actually alloys, or mixtures of metals.
Neodymium magnets, for instance, combine neodymium, iron, and boron to create exceptionally strong permanent magnets. Ferromagnetic materials are further categorized by their ability to retain a magnetic field once magnetized. Materials used to create permanent magnets, such as hardened steel or rare-earth alloys, are called “hard” magnets because they are difficult to demagnetize.
Conversely, “soft” ferromagnetic materials, like pure iron, are easily magnetized and demagnetized, making them suitable for temporary electromagnets and transformer cores. The magnetic properties of these materials are highly sensitive to temperature. Each ferromagnetic substance has a specific temperature, known as the Curie Point or Curie temperature, above which its permanent magnetic properties vanish.
Once heated past this point, the material undergoes a phase transition, and the strong, cooperative magnetic alignment is destroyed by thermal energy. Above the Curie Point, a ferromagnetic material transitions into a paramagnetic state, losing its ability to hold a permanent magnetic field. For example, iron loses its ferromagnetism at approximately 770°C, while nickel’s Curie Point is much lower, around 360°C.
The Internal Mechanism of Magnetism (Magnetic Domains)
The strength of ferromagnetism is rooted in the behavior of electrons within the material’s atoms. Electrons possess an intrinsic property called spin, which causes them to behave like tiny spinning charges, each generating a minute magnetic field called a magnetic moment. In most materials, these electron spins are randomly oriented or are paired with an oppositely spinning electron, causing their magnetic moments to cancel out. In a ferromagnetic material, however, the atomic structure contains unpaired electrons whose spins align in the same direction due to a quantum mechanical effect known as exchange coupling.
This strong, short-range force causes the magnetic moments of neighboring atoms to lock into parallel alignment. The alignment does not occur uniformly across the entire material, but rather in distinct, microscopic regions called magnetic domains. Within a single magnetic domain, all the atomic magnetic moments point in the same direction, creating a region that is fully magnetized.
In an unmagnetized piece of metal, the magnetic domains are oriented randomly, with the magnetic field of one domain canceling out the fields of its neighbors, resulting in no net external magnetic field. When an external magnetic field is applied, two things happen to these domains. First, domains aligned with the external field will grow larger, expanding at the expense of less favorably oriented domains. Second, the magnetic moments within the domains that are not aligned will rotate until they point in the direction of the external field.
This collective realignment creates a strong net magnetic field that characterizes ferromagnetism. When the external field is removed, the material’s internal forces keep the domains locked in their new, aligned state, resulting in a permanent magnet.
Beyond Ferromagnetism: Other Magnetic States
Ferromagnetism is contrasted by weaker forms of magnetic behavior found in all matter. The two other major categories are paramagnetism and diamagnetism, both of which are far too weak to create permanent magnets or be strongly attracted to them in everyday settings.
Paramagnetism is exhibited by materials that contain unpaired electrons, similar to ferromagnets, but the alignment of their magnetic moments is much weaker. While paramagnetic materials are weakly attracted to a magnetic field, the alignment is temporary. Thermal energy quickly randomizes the magnetic moments when the external field is removed, meaning these materials cannot retain a permanent magnetic state.
Examples of paramagnetic substances include aluminum, platinum, and even liquid oxygen. The other common magnetic state is diamagnetism, a property present in all matter, including water, wood, and most organic compounds. Diamagnetic materials contain no unpaired electrons; all their electron spins are paired, causing their magnetic moments to cancel out naturally. When placed in an external magnetic field, a weak opposing magnetic field is induced within the material, causing it to be slightly repelled.
Unlike ferromagnetism and paramagnetism, the diamagnetic response always opposes the applied field, regardless of the material. Copper, gold, and most gases are examples of materials that primarily exhibit this slight magnetic repulsion.