All matter responds to a magnetic field, though the interaction is often too subtle to notice without specialized equipment. Atomic forces govern how a material interacts with an external magnet, determining the strength and direction of the resulting magnetic effect. These atomic-level interactions sort materials into distinct categories based on their magnetic characteristics. The two most common forms of this behavior, present in nearly all substances, are diamagnetism and paramagnetism.
Diamagnetism Explained
Diamagnetism is a fundamental property of all matter, although it is often masked by stronger magnetic effects. A material is classified as diamagnetic when it exhibits a weak repulsion from an external magnetic field. This behavior stems from the fact that all electrons within the atoms are paired, causing their individual magnetic moments to cancel out, meaning the atom has no net permanent magnetic moment. When the material is placed within an external magnetic field, the field induces a slight, temporary change in the electrons’ orbital motion, creating a small magnetic moment. This induced moment is always opposite to the external field, causing the weak repulsion, and vanishes immediately once the field is removed.
Paramagnetism Explained
Paramagnetism describes materials that are weakly attracted to an external magnetic field. This attraction is a result of the presence of one or more unpaired electrons within the substance, which create a permanent, small magnetic moment (dipole) in each atom. In the absence of an external magnetic field, these atomic dipoles are randomly oriented due to thermal energy, so their combined magnetic effect cancels out. When an external magnetic field is applied, the dipoles align themselves slightly with the field, causing a net magnetization. This aligning effect is relatively weak due to thermal motion, and the attraction disappears immediately when the external magnetic field is removed.
Key Differences in Magnetic Response
Direction of Force and Field Effect
The most immediate difference is the direction of the force experienced in an external field. Paramagnetic materials are weakly attracted to the field, while diamagnetic materials are subtly repelled. This directional difference translates directly to how the material affects the magnetic field passing through it. A paramagnetic material slightly strengthens the field because its induced magnetic moments align with the external field. Conversely, a diamagnetic material slightly weakens the field because its induced magnetic moment opposes the external field.
Influence of Temperature
The influence of temperature also distinguishes the two behaviors. Diamagnetism is generally independent of temperature because the underlying mechanism involves the stable orbital motion of all electrons. Paramagnetism, however, is inversely dependent on temperature. As the temperature increases, the randomizing effect of thermal energy makes it harder for the external field to align the atomic magnets, which reduces the material’s magnetic attraction.
Common Examples of Magnetic Behavior
Many common substances exhibit diamagnetism, including water, wood, copper, and gold. Most organic compounds and biological systems are also generally diamagnetic, as they are composed of molecules with all paired electrons. A variety of metals and molecules display paramagnetism due to their electron structure. Aluminum, magnesium, and platinum are common paramagnetic metals, while liquid oxygen is a notable molecular example that can be visibly suspended between the poles of a strong magnet.