A Null-Coil Pendulum Magnetometer

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Abstract
A null‐method magnetometer is described for the measurement of magnetization of small single crystals of polycrystalline specimens of ferromagnetic materials. It may also be used for measurements on para‐ and diamagnetic materials. The specimen is placed in an inhomogeneous magnetic field inside a ``null‐coil'' of known geometry, and the current through the coil is adjusted so as to reduce the net magnetic moment of coil and specimen to zero. This coil is rigidly attached to the lower end of a sensitive pendulum and the null‐position of the pendulum is observed with the aid of a projection‐microscope. This method eliminates the necessity of measuring the force on the specimen and the gradient of the magnetic field. The conditions are discussed under which the absolute error may be reduced to arbitrarily small values. The secondary field arising from the current in the null‐coil is, in general, negligible; however, a simple method is described for its elimination.

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