Magnetism is a fundamental force that influences how certain materials interact, causing them to attract or repel. Understanding which materials respond to magnetic fields and the underlying reasons provides insight into magnetism’s pervasive presence in everyday life.
The Materials Magnets Attract
Magnets primarily attract a specific group of materials known as ferromagnetic substances. The most common examples of these materials are the metals iron, nickel, and cobalt. Many alloys, which are mixtures of metals, also exhibit strong magnetic attraction if they contain a significant amount of these ferromagnetic elements. Steel, for instance, is an alloy primarily composed of iron and often displays strong magnetic properties. These materials are widely used in various applications, from construction to electronics, due to their inherent magnetic responsiveness.
The Science Behind Magnetic Attraction
The ability of a material to be attracted to a magnet stems from its atomic structure, specifically the behavior of its electrons. Within the atoms of ferromagnetic materials, electrons possess a property called “spin,” which generates tiny magnetic fields. In most materials, these electron spins are paired and oriented in opposite directions, causing their magnetic fields to cancel each other out.
However, in ferromagnetic materials, some electrons remain unpaired and align their spins in the same direction. These aligned electron spins create small, distinct regions within the material called magnetic domains. In an unmagnetized ferromagnetic object, these domains are randomly oriented, and their magnetic effects cancel out overall.
When an external magnetic field is applied, these randomly oriented magnetic domains within the material begin to align with the external field. This alignment causes the individual magnetic moments of the atoms to sum up, creating a net magnetic field within the material that is strongly attracted to the external magnet. This process makes the material temporarily magnetic, and in some cases, it can even become a permanent magnet itself.
Materials Magnets Do Not Attract
Many materials do not exhibit strong magnetic attraction. These include metals such as aluminum, copper, brass, lead, gold, and silver, and non-metallic substances like wood, plastic, glass, and rubber. The primary reason these materials are not strongly attracted to magnets is related to their electron configurations.
Unlike ferromagnetic materials, these non-magnetic substances either lack unpaired electrons or their electron spins are arranged in a way that their magnetic fields cancel each other out. Even if they have individual magnetic moments, these moments are either randomly oriented and cannot be easily aligned by an external magnetic field, or they produce only a very weak response. Some materials, known as diamagnetic substances, are even very weakly repelled by magnets.
Everyday Magnetic Observations
Magnetic properties are observable in many common objects. For instance, not all stainless steel is magnetic, even though it contains iron. The magnetic behavior of stainless steel depends on its specific composition and crystal structure. Austenitic stainless steels, which contain higher levels of nickel and manganese, are generally non-magnetic because their atomic arrangement prevents the alignment of magnetic domains. In contrast, ferritic and martensitic stainless steels, which have different internal structures, are magnetic.
Refrigerator doors seal tightly due to magnetic strips often containing iron. Coins, depending on their metallic composition, may or may not be attracted to magnets; for example, many US coins are non-magnetic, while some international coins contain nickel and are. Magnets are also integral to electric motors, speakers, and the magnetic strips on credit cards.