Exchange anisotropy in MBE grown MnPt/NiFe bilayers

Exchange anisotropy has been investigated by torque magnetometry for MnPt(30 nm)/NiFe(5 nm) bilayers grown by the MBE method on MgO(001), SrTiO3(001), and MgO(lll) substrates, In-situ reflection high-energy electron diffraction observation and ex-situ X-ray diffraction measurements revealed that the MnPt layers have chemical order and have (100) uncompensated and (111) compensated plane parallel to the film plane, respectively for (001) and (111) substrate orientation. In MnPt/NiFe/SrTiO3(001) torque components of unidirectional and uniaxial anisotropies have been observed, while in NiFe/MnPt/MgO(001) both the anisotropies almost disappeared and a torque curve with four fold symmetry was observed. This torque curve seems to be closely related with the crystal anisotropy of MnPt.