Reversal modes of the multilayer exchange-spring magnet

A one-dimensional micromagnetic model of the multilayer exchange-spring magnet is utilized for calculating the analytical expression of the differential susceptibility at the nucleation field in terms of structural parameters. The phase diagram in the plane of half-layer thicknesses is given for a Sm–Co/Fe multilayer, showing the critical line of χc→∞, which is the boundary for the irreversible demagnetization mode. For thin layers the optimum soft-phase volume fraction is deduced