  An AC susceptometer operating in the range of 10 Hz to 100 kHz and at room
temperature is designed, built, calibrated and used to characterize the
magnetic behaviour of coated magnetic nanoparticles. Other weakly magnetic
materials (in amounts of some millilitres) can be analyzed as well. The setup
makes use of a DAQ-based acquisition system in order to determine the amplitude
and the phase of the sample magnetization as a function of the frequency of the
driving magnetic field, which is powered by a digital waveform generator. A
specific acquisition strategy makes the response directly proportional to the
sample susceptibility, taking advantage of the differential nature of the coil
assembly. A calibration method based on conductive samples is developed.
