Magnetic susceptibility is a measure of a material's response to an external magnetic field H. Equilibrium magnetization characteristics M(H) are obtained by sweeping a DC magnetic field, whereas the magnetization's dynamic properties are captured by an AC component. For small AC excitations, the susceptibility is linearly proportional to the magnetic field. AC susceptibility measurements are used for:
- Fast magnetization characterization;
- The study of non-equilibrium processes; and
- Capturing small changes caused by magnetization dynamics or magnetic phase transitions.
Typical samples are magnetic materials and superconductors, as well as samples with time-varying magnetic properties that require the high temporal resolution afforded by the AC technique.