Magnetic susceptibility is a dimensionless parameter that measures the extent to which a material becomes magnetized when subjected to an external magnetic field. It is a property of magnetic materials that indicates their responsiveness to an applied magnetic field and helps classify materials based on their magnetic behavior.
Magnetic susceptibility (χ) is defined as the ratio of the magnetization (M) of a material to the applied magnetic field (H) that induces the magnetization:
χ = M / H
The value of magnetic susceptibility can be positive or negative, depending on the magnetic properties of the material:
- Paramagnetic materials: These materials have a positive magnetic susceptibility (χ > 0). When an external magnetic field is applied, their magnetic moments tend to align with the field, resulting in a net magnetization in the same direction as the applied field. However, the magnetization is typically weak and disappears when the external field is removed. Examples include aluminum, platinum, and some rare-earth elements.
- Diamagnetic materials: These materials exhibit a negative magnetic susceptibility (χ < 0). In the presence of an external magnetic field, their magnetic moments align opposite to the applied field, creating a weak magnetization that opposes the external field. The magnetization disappears when the field is removed. Examples of diamagnetic materials include copper, silver, and bismuth.
- Ferromagnetic, ferrimagnetic, and antiferromagnetic materials: These materials have a more complex relationship between magnetization and the applied magnetic field, which cannot be described simply by a constant magnetic susceptibility value. Their magnetic behavior arises from interactions between neighboring magnetic moments, leading to spontaneous magnetization even in the absence of an external magnetic field.
