The adiabatic temperature changes accompanying the magnetization of ferromagnetic materials in low and moderate fields

A new and relatively simple method is described for the measurement of the heat changes which accompany magnetization processes in fields of the order of a few hundred oersteds. The adiabatic changes in temperature of a rod which occur when the latter is taken step-by-step through a hysteresis cycle are measured by a series of thermocouples of which the "hot" junctions are directly attached to the rod. The temperature-measuring system is capable of detecting changes in temperature of the order of 10 -6 deg. c., and its sensitivity is such that 1 mm. scale deflection corresponds to the absorption or liberation of about 330 ergs per c.c. in the specimen, deflections of 0.1 mm. being easy to read. Experiments made with pure annealed and hard-drawn nickel and with certain nickel-iron alloys, strained and unstrained, are described, and many graphs are given to show the observed temperature changes as functions of the intensity of magnetization and of the applied field. The results provide a very effective proof of Warburg's law, but their main importance is that they enable a detailed analysis of the energy changes accompanying magnetization to be made. They show that Becker's views on magnetization processes in ordinary ferromagnetic materials are essentially correct, but do not support Preisach's conception of the formation of demagnetization nuclei in the case of extremely soft ferromagnetic materials.