Characterization and modeling of the demagnetization processes in exchange-coupled SmCo 5 / Fe / SmCo 5 trilayers

The demagnetization processes in epitaxially grown ${\text{SmCo}}_{5}/\text{Fe}/{\text{SmCo}}_{5}$ trilayers have been analyzed in the framework of a one-dimensional micromagnetic model, exploiting the well-defined orientation of the easy magnetization axis present in both ${\text{SmCo}}_{5}$ layers. The applied magnetic field is considered along easy, hard, and tilted directions. For the case of hard direction, the nucleation field equation and the analytical expression of the critical susceptibility are given. Due to the observed separate switching behavior of the two hard layers in the realized trilayers, the analysis also considers demagnetization processes in which the two hard layers have opposite magnetic polarization. Calculations based on the nominal values of the magnetic and geometric parameters for the ideal symmetric trilayer are only in qualitative agreement with the corresponding experimental curves. In order to explain the discrepancies, the influence of variations in the parameters has been deeply analyzed, as well as the effect of a distribution of tilting angles of the hard layers anisotropy axes. In addition, we have extended the model to treat the case of a real asymmetric trilayer, characterized by slightly different anisotropy properties of the two hard layers, and we have derived the corresponding nucleation field equation for the case of easy direction. This analysis shows that a better agreement between calculations and measurements concerning the reversible behavior of the trilayers can be achieved by slightly modifying the nominal soft layer thickness and by assigning different tilting angles to the hard layers. Moreover, it shows that the remaining discrepancies can be ascribed to imperfections, which cannot be considered in detail in the one-dimensional model.