A mutual inductometer bridge method has been developed to measure the reversible susceptibility κ r of a ferromagnetic by the application of small alternating fields to specimens in the form of long wires. The corrections which must be applied because of the finite amplitude of the alternating field and for eddy current effects are investigated and an overall accuracy within about 1% is attained. Typical results are given for Swedish iron which show a marked increase in susceptibility after decarburizing and annealing, and this is discussed in relation to the ideas of Néel. By the evaluation of ∫ κ r dH over a suitable range of field, the minimum contribution of reversible processes to the total change in magnetization is estimated and found to vary from 10 to 20% for the specimens of iron and nickel examined Finally an investigation has been made into the statement of Gans that reversible susceptibility is a unique function of intensity of magnetization and independent of the magnetic history of the specimen; the statement is shown to be true only for specimens which have been brought into a given state of magnetization round a hysteresis cycle, and then only for the regions of higher magnetization.
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Tebble et al. (1950) studied this question.