AC susceptibility technique:

• AC susceptibility is the differential dM/dH response of the magnetization (M) of the sample to an oscillating magnetic field (H). Operating frequencies (f) often vary from 1 Hz to 10 kHz.

• Low amplitude of the driving field is utilized to probe the undisturbed ground state of the materials.

• AC susceptibility is a complex value and reads as

where the real component χ' related to the reversible magnetization process, stays in phase with the oscillating magnetic field . The imaginary component χ” is related to the losses due to the irreversible magnetization process and energy absorbed from the field, as the phase shift θ may happen in magnetization.

This provides

Components or real and imaginary of magnetic samples are measured as functions of temperature, frequency, and amplitude of driving field, static bias field, applied pressure, and other external parameters.