3. Measuring magnetic fields

The measurement of magnetic fields is an essential part of any experimental characterization of magnetic materials. Whether applied, generated by the material itself or present in the environment, no meaningful characterization can be made without their precise determination. A classic method for revealing and measuring a magnetic field is to use a coil, across which a fem proportional to the time derivative of the flux embraced is detected, in accordance with the Maxwell-Faraday law of induction. Detection of continuous fields by this method requires either field switching or coil movement (extraction, rotation, reversal) to obtain a controlled flux variation. The linearity, accuracy, wide frequency and field range, rusticity and low cost of this type of device all make the fluxmeter method ideal for measuring alternating fields. There are, however, situations in which direct field measurement...