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Helmholtz coils can be used for the measurement of open-circuit magnetization of most permanent magnet materials. The author describes the physics of the measurement, lists the materials that can be measured, derives the coil constant, and derives a correction factor for the measurement of arc magnets. A measurement is made by placing the magnet at the center of the coils, and zeroing the integrating voltmeter or fluxmeter. The magnet is then removed from the coil, parallel to the coil axis, to a distance such that the sample has no influence on the reading, typically 75 to 100 cm. The open-circuit magnetization of the sample is related to the time-integrated voltage.>
Stanley R. Trout (Fri,) studied this question.