Hysteresis and magnetic viscosity in a Nd-Fe-B permanent magnet

Measurements have been made of the hysteresis of thermally and field-demagnetized sintered specimens of a Nd-Fe-B permanent magnet. Sets of minor hysteresis loops have been obtained by a gradual increase in the maximum applied field thus enabling the intrinsic coercivity and the remanence coercivity to be plotted as a function of the maximum applied field. These results show that there is a threshold field which must be exceeded before a substantial coercivity can be obtained. Measurements of the magnetic viscosity have also been made which show that the change in the magnetization in a static reverse field varies with the logarithm of the time for which the field is applied. The slopes of the curves depended on the applied field; the maximum slope was observed when the applied field was equal to the coercivity.