What is paramagnetism?

Paramagnetism is a physical phenomenon that describes the behavior of materials in the presence of an external magnetic field. It is a form of magnetic behavior in which atoms or molecules react weakly to the magnetic field due to their electronic structure.

How does paramagnetism differ from other types of magnetism?

Unlike ferromagnetism, where materials show strong magnetic attraction, and diamagnetism, where materials are weakly repelled, paramagnetism only occurs under the influence of an external magnetic field. In this case, the atoms or molecules of the material are temporarily magnetized and align their magnetic moments parallel to the external field.

When does paramagnetism occur?

The cause of paramagnetism lies in the unpaired electrons in the atoms or molecules of the material. These electrons have both a magnetic spin and a magnetic moment. In a material without an external magnetic field, the magnetic moments of the unpaired electrons are randomly oriented, so the material as a whole has no magnetic properties.

However, when an external magnetic field is applied, the unpaired electrons experience a force that causes them to align parallelly to the field. This results in a weak net magnetisation of the material, as the number of parallel aligned magnetic moments is slightly different from the anti-parallel aligned moments.

The strength of a material's paramagnetism depends on the number of unpaired electrons. The more unpaired electrons a material has, the stronger its paramagnetic response to an external magnetic field. The opposite is true if there are fewer unpaired electrons.

Some examples of paramagnetic materials are oxygen, aluminum, platinum and gadolinium. These materials show a weak magnetic attraction in the presence of a magnetic field, but immediately return to unmagnetised states as soon as the magnetic field is removed.

What are applications of paramagnetism?

Paramagnetism has various practical applications. In chemistry and materials science, for example, it is used to characterize compounds and study their magnetic properties. Paramagnetism is also used for medical purposes in magnetic resonance imaging (MRI).