Investigation of the exchange mechanism in NiFe-TbCo bilayers

The origin of the interfacial exchange coupling that exists in NiFe-TbCo bilayer thin films has been investigated through high resolution Kerr microscopy and VSM studies. Based on these experimental observations, a new model of the exchange mechanism for in-plane, ferromagnetic-perpendicular ferrimagnetic materials is developed. It is proposed that the local anisotropy in the TbCo layer varies from in-plane at the interface to perpendicular at the top surface. The relative magnitude of the exchange effect calculated with average TbCo Ku values, agrees with experimental data. The predicted dependence of the exchange field on NiFe and TbCo layer thickness also fit the experimental data.