Magnetic Hysteresis and Demagnetizing-Field Correction for Rare Earth Magnet Materials

The standard method for measuring magnetization, using a closed magnetic circuit, cannot be applied to rare earth magnet materials with very high coercivity. Hence in this paper we examine an open magnetic circuit method in a steady high magnetic field, in which correction for the demagnetizing field is important. We measured hysteresis curves for some commercial rare earth magnet materials by using cylindrical samples with various dimension ratios. The correction for the demagnetizing field gives a reasonable result for bonded magnets, whereas even the intrinsic coercivity seems to depend on the sample shape in the case of sintered magnets. Therefore, it is necessary to reconsider the correction for the demagnetizing field as well as the standard specifications of rare earth magnet materials.