Interface roughness and exchange bias - Coercivity ratio in Pulsed-DC magnetron sputtered NiFe/IrMn/CoFe exchange bias trilayers

Abstract

Ta/Ru/Ta/Ni81Fe19/Ir20Mn 80/Co90Fe10 exchange bias multilayer was grown by using pulsed DC unbalanced magnetron sputtering technique. The deposition pulse frequency of the NiFe seed layer has been varied between 10 - 50 kHz, by keeping all parameters of the remaining layers constant. The evolutions of the grain size, texture, interface roughness and the exchange bias (Hex) and coercivity fields (Hc) including the Hex/Hc ratio have been systematically investigated. Grain size of the IrMn layer changes in the range of 8.9 nm-22 nm by constant layer thicknesses. The H ex is directly affected by the IrMn grain size for the bottom NiFe/IrMn interface, while it remains nearly insensitive to the grain size for the top IrMn/CoFe interface. The Hex at the NiFe/IrMn interface is largest if the grain size of the IrMn layer is same as the IrMn layer thickness. A direct relationship between the Hc and grain size values was not observed; however, the Hc is predominantly affected by the roughness of NiFe/IrMn and IrMn/CoFe interfaces. Results reveal that the texture and interface roughness plays an important role on the Hex/Hc ratio and deposition conditions for the ferromagnetic layer can be optimized using the variable deposition pulse frequency for a high Hex/H c ratio in the investigated trilayer EB system.