In ${\mathrm{Gd}}_{40}{\mathrm{Fe}}_{60}/{\mathrm{Tb}}_{12}{\mathrm{Fe}}_{88}$ exchange-coupled bilayer system, both negative and positive exchange bias, depending on cooling field, are observed. A full enlightenment of the magnetic configurations adopted by the system is obtained through micromagnetic calculations in agreement with magnetization and susceptibility measurements. Magnetization shifts and exchange bias fields are then quantitatively correlated to the presence of a frozen interface domain wall. This model may be transposed to antiferromagnetically exchange coupled antiferromagnetic/ferromagnetic $(\mathrm{Fe}/{\mathrm{FeF}}_2$ or $\mathrm{Fe}/{\mathrm{MnF}}_2)$ systems.

• Received 12 May 2003

DOI:https://doi.org/10.1103/PhysRevB.68.140404