Magnetization process in ferromagnetic bilayer with exchange coupling through a pinhole

The magnetization process has been investigated for SmCo5/SiO2/Fe19Ni81 trilayer films, in which the exchange coupling between hard-ferromagnetic SmCo5 and soft-ferromagnetic Fe19Ni81 layers is controlled by the size (1-100 mum in diameter) of a pinhole penetrating the SiO2 layer. The observed magnetization curve indicates that the magnetization reversal in the SmCo5 layer consists of a nucleation around the pinhole and the propagation of the domain wall. This can be responsible for the suppression of the coercivity induced by the coupling through the pinhole. Variation of the magnetization curve with the size of the pinhole can be argued from the viewpoint of the simple domain nucleation model. (C) 2002 American Institute of Physics.