Magnetism is an invisible force of nature that governs the behavior of materials within a magnetic field. This field exerts a force on matter, but not all substances respond the same way. A material’s magnetic response depends entirely on its internal atomic and electronic structure, leading to reactions ranging from powerful attraction to subtle repulsion. Understanding which materials are attracted to magnets requires looking closely at the specific composition of a substance and how its electrons are arranged.
The Materials of Strong Attraction
The materials that exhibit a strong, easily observable attraction to a magnet are known as ferromagnets. This class of substances is what most people think of when they consider magnetic attraction. Only a handful of elements are ferromagnetic at room temperature: iron, nickel, and cobalt.
Steel, an alloy of iron and carbon, retains strong magnetic properties. Certain rare-earth elements, such as gadolinium and dysprosium, also display this attraction, though they only do so well below room temperature.
Ferromagnets are defined by their ability to become magnetized and retain that magnetization even after the external field is removed, making them suitable for creating permanent magnets used in motors, refrigerators, and speakers.
Understanding Magnetic Attraction
The intense attraction seen in ferromagnetic materials is rooted in the quantum behavior of electrons. Every electron possesses spin, which effectively turns it into a tiny, subatomic magnet with its own magnetic moment. In most atoms, electrons are paired, causing their magnetic moments to cancel each other out.
Ferromagnetic atoms have unpaired electrons, meaning their individual magnetic moments do not cancel and instead create a net magnetic field. Within the material, these atomic magnetic moments spontaneously align in the same direction over microscopic regions called magnetic domains. A domain is a self-contained area where all the atomic magnets point coherently.
In an unmagnetized piece of iron, the domains are oriented randomly. When an external magnet is brought near, the domain walls shift, and the internal fields rotate to align with the applied field. This alignment increases the material’s net magnetic field, resulting in powerful attraction. Once the external field is removed, many domains remain aligned, which is why the material stays permanently magnetized.
Weakly Attracted Materials
Beyond ferromagnets, many substances exhibit a much weaker magnetic interaction known as paramagnetism. These materials are only slightly attracted to a magnetic field, and they lose this attraction the moment the external field is removed. The underlying cause is similar to ferromagnetism, as the atoms possess unpaired electrons and a net magnetic moment.
The difference lies in the absence of the collective ordering seen in magnetic domains. In a paramagnetic material, such as aluminum, platinum, or liquid oxygen, the atomic magnetic moments are randomly oriented due to thermal agitation. When an external field is applied, the moments briefly align parallel to the field, creating a weak induced magnetic field in the same direction.
This temporary alignment causes the material to be weakly drawn toward the magnetic source. Because the attractive force is faint, it is usually only detectable using sensitive laboratory instruments. When the external magnetic field is removed, thermal energy quickly randomizes the alignment of the magnetic moments, and the material instantly returns to its non-magnetic state.
Materials That Are Repelled
The final category of magnetic response is diamagnetism, where materials are weakly repelled by a magnetic field. This is a universal property found in all matter, though it is usually masked by stronger effects. Diamagnetic materials are characterized by having all electrons paired up, meaning they have no permanent net magnetic moment.
When a magnetic field is applied to a diamagnetic substance, it causes a slight shift in the orbital motion of the electrons. This change generates a tiny, induced magnetic field that opposes the external field, a process known as Faraday’s Law of Magnetic Induction. Because the induced field points in the opposite direction, the material experiences a weak repulsive force.
This weak repulsion is observed in many common substances, including water, gold, copper, and most organic compounds like plastic and wood. Although the effect is minuscule, it can be demonstrated using powerful magnets, which can cause a frog (which is mostly water) to levitate.
The repulsion is independent of temperature and is a consequence of how electrons in any material respond to an external magnetic field.