Magnetism is a physical phenomenon where materials exert attractive or repulsive forces through a magnetic field. This field is an area of influence surrounding a magnet or an electric current, produced by the movement of electric charges. The force acts on other moving charges or on materials that possess magnetic properties at the atomic level. Understanding how different substances react to this force reveals distinct categories of magnetic behavior.
Ferromagnetic Materials
This powerful attraction is found in substances containing the elements iron, nickel, and cobalt. These three elements and their alloys are the primary materials that will strongly stick to a typical permanent magnet.
The reason for this intense pull lies in their atomic structure, which allows them to become highly magnetized when placed in a magnetic field. Common alloys, such as various types of steel, also demonstrate this characteristic because they are primarily composed of iron. Many objects used daily, including paperclips, screws, refrigerators, and car bodies, utilize this strong magnetic property. These materials can even retain their own magnetism after the external field is removed, becoming permanent magnets themselves.
Materials That Do Not Respond to Magnets
Many common materials are unaffected by a magnet when a standard household magnet is brought near. This group includes substances like plastics, wood, paper, glass, and most liquids. Even many metals do not exhibit a strong magnetic pull.
Metals such as aluminum, copper, gold, silver, and zinc are non-responsive to magnets in normal settings. Their lack of response is due to their atomic arrangement. Unlike the strongly attracted materials, the electrons within these substances are configured in a way that prevents the internal alignment needed for a strong magnetic response. This explains why an aluminum soda can or a copper coin will not stick to a refrigerator magnet.
Subtle Forms of Magnetic Interaction
All substances interact with a magnetic field, even if they are not strongly attracted. These weaker responses fall into two main categories: paramagnetism and diamagnetism. Paramagnetic materials are very weakly attracted to a magnetic field, an effect so slight it is usually only detectable using sensitive laboratory instruments.
Examples of paramagnetic substances include aluminum, magnesium, and liquid oxygen. In these materials, the magnetic moments of individual atoms align slightly with the external field, resulting in the faint attraction. Conversely, diamagnetic materials exhibit a weak repulsion from a magnetic field. Water, carbon, copper, and bismuth are examples of substances that display this slight repulsive effect. In diamagnetic substances, the magnetic field induces a change in the electrons’ motion that weakly opposes the external field.
The Underlying Cause of Magnetic Behavior
The magnetic behavior of any material stems from the movement of its electrons at the atomic level. Every electron acts like a tiny magnet due to its spin, which generates a magnetic moment. In most materials, electrons are paired up, and the magnetic moment of one electron is canceled out by its partner spinning in the opposite direction.
Strong magnetic attraction is observed in materials where electrons are left unpaired, resulting in a net magnetic moment for the atom. In iron, nickel, and cobalt, these atomic magnetic moments spontaneously align within small regions called magnetic domains. When a magnet is introduced, the boundaries of these domains shift, causing the domains to align with the external field and resulting in strong attraction. Materials that show only subtle magnetic effects, like paramagnets, have unpaired electrons, but the atomic magnetic moments are randomly oriented and do not form these large, cooperative domains.