AC Susceptometry gives information on how rapidly the magnetization in the material can change when an external magnetic field is applied. The results of dynamic magnetic susceptometry give valuable information about the magnetic properties of magnetic particles that are being used in many applications, such as biomedical applications and in magnetic information carriers. Dynamic susceptometry is a valuable tool in achieving a stable magnetic-particle production process. Dynamic susceptometry is also used in the general magnetic characterization of materials and in magnetic soil measurements in geophysics, archeology and prospecting.
We have developed the DynoMag system, a unique, sensitive and portable AC susceptometer. This instrument detects the AC susceptibility, also called the frequency-dependent susceptibility, up to 200 kHz. We are developing a high-frequency AC susceptometer in order to measure the AC susceptibility in the MHz region.
AC susceptometry is a valuable magnetic tool for understanding magnetic materials as it provides information on how rapidly magnetization is building up. All types of magnetization processes – for example, magnetization reversal in magnetic singledomains (Néel relaxation), random rotation of particles in a carrier liquid containing thermally blocked single domains (Brownian relaxation), domain-wall motion in polydomain materials, and or magnetic resonances of the magnetization in the material – create a specific pattern in the AC susceptibility. For particles undergoing Brownian relaxation, the size distribution of the particles can be determined from empirical data.
The dynamic magnetic properties can also be revealed by measuring the magnetization change versus time. We are also working with pulsed magnetic fields in order to determine magnetization decay, the result being much more rapid measurement of the dynamic magnetic processes in the material than can be done by measuring the response in the frequency domain.