Magnetic susceptibility (χ_m) is a measure of the degree to which a material can be magnetized in an external magnetic field. It is positive for a paramagnetic or ferromagnetic material and negative for a diamagnetic material. χ_m is a dimensionless (unitless) quantity. It is a fundamental property of materials that is used extensively in various fields such as geology, physics, chemistry, and materials science.

 

Magnetic susceptibility is the relative permeability (i.e., the ratio of the magnetic permeability of a medium to that of a vacuum), minus one: χ_m= μ_r – 1.

 

In general, materials with positive magnetic susceptibility are those that are attracted to a magnetic field, while materials with negative magnetic susceptibility are those that are repelled by a magnetic field. A material with a magnetic susceptibility of zero is said to be diamagnetic, meaning that it does not interact with a magnetic field.

 

The magnetic susceptibility of a material depends on a number of factors, such as the type of atoms or ions present in the material, their electronic configuration, and the bonding between them. For example, materials with unpaired electrons, such as iron, nickel, and cobalt, have a high magnetic susceptibility because their electrons can easily align themselves with an external magnetic field. In addition, the temperature and pressure of a material also affect its magnetic susceptibility. Generally, the magnetic susceptibility of a material decreases as the temperature increases, and increases as the pressure increases.

 

Magnetic susceptibility has many practical applications. In geology, it's used to study the magnetic properties of rocks and minerals. By measuring the magnetic susceptibility of rocks and minerals, geologists can gain insights into the geological history of a particular region, such as the presence of minerals or the occurrence of geological events like earthquakes and volcanic eruptions.

 

In materials science, magnetic susceptibility is used to study the magnetic properties of materials, such as metals, alloys, and ceramics. By measuring the magnetic susceptibility of these materials, scientists can gain insights into their electronic and magnetic properties, which can be useful for developing new materials with specific magnetic properties.