How are the magnetic properties of permanent magnets specified?
Magnet block and powder are measured using specialized test instrumentation which, in general terms, determine how a magnet responds to a changing magnetic field, because that is what happens in most “magnetic circuits” or applications. The vast majority of applications require knowledge of the “demagnetization curve” of a magnetic material – this is a fraction of the full “hysteresis loop” and is a measure of how much magnetism is left in the material as an increasing reverse magnetic field is applied to it. There are other names for this measurement, such as the “second quadrant of the hysteresis loop”. If an engineer understands the demagnetizing conditions that are imposed on the magnet by the application, then the demagnetization curve can be used to predict the performance of the magnetic circuit. The temperature of the magnet in the circuit must be known and the demagnetization curve at that temperature must be used if accurate results are to be obtained – the properties of all
