Comparison on the structure and exchange bias in Co/MnPt and MnPt/Co polycrystalline films on glass substrates

Structure and magnetic properties of sputter-prepared Co(5 nm)/MnPt(20 nm) and MnPt/Co polycrystalline films with various annealing temperatures (T) have been compared. XRD and TEM analysis show that MnPt is more compressive in film plane for Co/MnPt than MnPt/Co at as-deposited state. Large HE of 464-560 Oe are attained in two series films through proper thermal process of post annealing and cooling in external magnetic field. The increase of HE with T is mainly dominated by the ordering degree of MnPt layer and the roughness of the interface. As compared to MnPt/Co film (T = 250 °C), Co/MnPt film with more compressive in film plane exhibits L10-ordering, the onset of stress release, and the optimized HE at lower T = 200 °C. Higher HE for MnPt/Co film at T = 250 °C (560 Oe) than Co/MnPt film T = 200 °C (464 Oe) might be related to grain growth for L10 phase. Nevertheless, higher annealing temperature leads to the interdiffusion, the roughened surface and therefore the decrease of HE and Hc. This study provides useful information to fabricate exchange-bias system with L10-MnPt as an antiferromagnetic layer.