A method of measuring magnetic susceptibilities

Abstract

Among the different methods which can be used to measure the magnetic susceptibility of feebly magnetic substances, the most practical, and those most frequently employed at the present time, depend essentially on the measurement of the force acting on the substance when placed in a non-uniform field. This force is given by the well-known formula F x = χ ∫ v 0 H d H/d x d V, where χ is the volume susceptibility, (H) is the magnetic field, d H/ d x is the gradient of the magnetic field in the direction x in which the force is measured at the site of a small element of volume ( d V). Corresponding to the wide range of susceptibility, and to the different physical states and conditions which occur, a number of methods of measuring this force have been developed. In all these methods, since they are based on the measurement of the force on the substance, and since it is by the displacement of the body that the force is measured, it is essential that the body should be movable. The force acting on the body is small, usually only a few dynes, and delicate methods have to be used for making the measurements, as, for instance, in the Curie-Faraday method where the substance is carried on a sensitive torsion balance.