Discontinuties of Magnetization in Iron and Nickel

Discontinuities of magnetization.---These have been observed in iron and nickel and recorded photographically. The number corresponding to a given small change of magnetizing force has been determined for different speeds of magnetization. For high speeds there appear to be more and smaller discontinuities as the speed is slightly reduced. If the speed is greatly reduced, however, there are fewer discontinuities in ordinary specimens than for high speeds. The length of the portion of material associated with each discontinuity is estimated to be 2 or 3 mm; the volume is of the order 10^-7 cm³.A method for determining the hysteresis loop of very small specimens.---The specimen, on an elastic support, is mounted on the axis of a solenoid and its deflection measured with a microscope when currents of varying magnitude flow through the solenoid. For a small piece of nickel wire it is found that the loop is made up of a few discontinuities separated by uniform changes of magnetization.Theory.---It is suggested that in different portions of the material different magnetostrictive effects may occur. Thus strains are set up which, when relieved discontinuously, produce the jumps of induction.