CHARACTERISATION OF HARD MAGNETIC MATERIALS

Roland Grössinger

   Different methods determining the hysteresis loop of permanent magnets are summarised. In industry the use of a hysteresograph (based on fluxmeters) within an electromagnet as a field source is most common. This is a magnetic closed system where no demagnetizing effects have to be considered. A Vibrating Sample Magnetometer (VSM) is a magnetically open system, but it offers a significantly higher sensitivity. If as a field source a superconducting coil is used fields up to 10 T are easy to get. The system with the highest sensitivity, which allows the measurement of single grains or thin films, is a SQUID-magnetometer. SQUID magnetometers are available with external fields up to 7 T, however such instruments are more common in scientific laboratories. A Pulsed Field Magnetometer (PFM) offers sufficient high external fields (10 T and more) together with a fast measuring system. Disadvantageous is that in such system time dependent effects such as eddy currents and magnetic viscosity may limit the achievable accuracy. However for a quality control a PFM is a very suitable instrument.

Keywords: hard magnetic materials, magnetometers, pulsed fields

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