Heat Effects in the Magnetization of Silicon Iron

Abstract

A brief description is given of the method used by Bates and his co-workers which permits the measurement of the thermal changes which accompany the step-by-step magnetization of ferromagnetic metals. The method has now been used to examine the behavior of 0.5 and 4 percent silicon iron in the untreated and annealed states when magnetized along the virgin curve and in cycles with fields up to 380 oersteds. In this work, some twenty copper-constantan thermocouples generate currents when a magnetic field acting on the ferromagnetic specimen is changed, and these are transmitted ballistically via a toroidal Mu Metal transformer to a highly sensitive moving coil galvanometer of long period. As the thermal changes in the present work were very small, a new technique had to be developed to deal with them. The measured thermal changes are plotted as functions both of the intensity of magnetization and of the effective magnetic field. The several errors and experimental difficulties, including asymmetry in thermal readings, stray induction effects, heating due to eddy currents, and thermal and electromagnetic disturbances experienced during the measurements are briefly discussed, and the methods used to overcome them are briefly outlined.