Thickness dependence of exchange anisotropy for (001) oriented Mn89Pt11/NiFe and Mn80Ir20/NiFe bilayers

Abstract Antiferromagnetic layer thickness dependences of exchange anisotropy for (0 0 1) oriented Mn 89 Pt 11 ( t AF  nm)/Ni 80 Fe 20 (5 nm) and Mn 80 Ir 20 ( t AF  nm)/Ni 80 Fe 20 (5 nm) were investigated. For Mn 89 Pt 11 /NiFe, the exchange bias field appeared at t AF ⩾5 nm. This critical thickness was found to be thicker than that of Mn 80 Ir 20 /NiFe ( t AF =3 nm). The thickness dependence of exchange bias field agreed well with that of 1-fold Fourier amplitude estimated from in-plane torque curves. The large coercivity of about 100 Oe was found for Mn 89 Pt 11 /NiFe at t AF =30 nm compared to that of Mn 80 Ir 20 /NiFe. The large coercivity in Mn 89 Pt 11 /NiFe bilayers seems to result from the large 4-fold anisotropy in their torque curve.