Paramagnetism

Paramagnetism is a form of magnetism where some materials are weakly attracted to an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied field. Unlike ferromagnetism, paramagnetism only exists in the presence of an external magnetic field. This behavior arises from the presence of unpaired electrons in the material's atoms or ions, which possess a magnetic dipole moment. When an external field is applied, these dipoles tend to align themselves, leading to a net magnetization. However, this alignment is often counteracted by thermal agitation, resulting in a relatively weak magnetic susceptibility, meaning the material’s ability to become magnetized is small. The strength of paramagnetism is usually temperature-dependent, decreasing as temperature increases because thermal energy disrupts the alignment of magnetic dipoles.

Paramagnetism meaning with examples

• Liquid oxygen, a classic example of a paramagnetic substance, visibly clings to a strong magnet due to its unpaired electrons. This attraction is a direct demonstration of paramagnetism. Its susceptibility, however, is much less than that of iron or other ferromagnetic materials, which exhibit much stronger magnetism.
• In medical imaging, paramagnetic contrast agents, such as gadolinium-based compounds, are used in MRI scans to enhance the visibility of tissues. These agents alter the relaxation times of water molecules, improving image contrast. The contrast agents' paramagnetism helps to produce a clear image.
• Certain transition metals, like platinum, exhibit paramagnetic properties. Their partially filled electron shells lead to unpaired electrons and therefore they display weak attraction to magnetic fields. Their susceptibility, though weak, is exploited in various scientific and industrial applications, such as chemical catalysts.
• The study of paramagnetism is important in materials science as it helps scientists understand the electronic structure and bonding characteristics of a given material. By measuring a material's magnetic susceptibility, researchers can determine the number of unpaired electrons, which gives information about its physical and chemical properties.
• Researchers exploit paramagnetism in various specialized applications. Examples are in magnetic separation techniques, such as separating magnetic particles or molecules. These specialized magnetic systems are an application that relies on the subtle attraction between magnetic fields and the presence of unpaired electrons.