Magnetic Hysteresis Loop Tracer Using Operational Amplifiers

A magnetic hysteresis loop tracer has been built to measure the magnetic properties of small cylindrical samples of nonconductive ferromagnets. Applied fields of 10 000 Oe peak amplitude are obtained from a water cooled solenoid driven at 60 Hz, and the change in flux is detected with a coil on the sample. Two operational amplifiers convert the input variables to analogs of the local field H and the induction B or magnetic intensity I. The sample area and demagnetizing factor are used as parameters, and a correction is made for the excess coil area. Tests indicate that correct loops are produced except when the demagnetizing factor and the excess coil area are both large. Application to the rapid determination of the magnetic properties of hard ferrites is illustrated. The apparatus may also be used to magnetize and demagnetize samples and measure the permeabilities in both states.