Reversible and irreversible magnetization in hybrid magnets

Magnetization reversal was studied in hybrid magnets consisting of ferrite and ribbons of the Magnequench alloy MQP-Q (Nd2Fe14B + alpha-Fe). Recent studies of demagnetization processes in permanent magnets have used two different methods for determining the reversible magnetization, often arriving at conflicting results. The reversible M-rev and irreversible M-irr magnetizations were determined here by the two different procedures: (i) In the dc demagnetization method, the demagnetization remanence is measured for reverse magnetic fields after saturation in the forward direction. Assuming the change in magnetization along the recoil curve is reversible, the remanent magnetization is identified with the irreversible magnetization M-irr. (ii) Alternatively, the intrinsic reversible susceptibility chi(rev)(i) was measured by defining it as the mean slope of a small minor loop performed after determining the time dependence of M. The reversible susceptibility was then integrated to obtain M-rev. Although the two procedures for determining M-rev are frequently considered equivalent, we discuss here the differences that arise when one or the other method is used. These differences may be important when magnetic materials are characterized using switching field distributions, Henkel plots, or delta M plots. (C) 2000 American Institute of Physics. [S0021-8979(00)08303-1].