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 st udies of demagnetization processes in permanent magnets have used two diffe rent methods for determining the reversible magnetization, often arriving a t conflicting results. The reversible M-rev and irreversible M-irr magnetiz ations were determined here by the two different procedures: (i) In the dc demagnetization method, the demagnetization remanence is measured for rever se 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 mea sured by defining it as the mean slope of a small minor loop performed afte r determining the time dependence of M. The reversible susceptibility was t hen integrated to obtain M-rev. Although the two procedures for determining M-rev are frequently considered equivalent, we discuss here the difference s 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].