Study of the influence of Nb buffer layer on the exchange coupling induced at the Co/IrMn interface

•Nb buffer layer favors smooth/rough Co/IrMn interfaces, depending on its thickness.•Double and single-like hysteresis loop features depend on the Nb thickness.•Co uniaxial anisotropy induced exchange-bias in as-deposited sample.•Uniaxial and exchange-bias anisotropy directions depend on the Nb thickness.•Thicker Nb favors non-collinear anisotropies, while thinner Nb favors collinear. Hybrid Nb(tNb)/Co(10nm)/IrMn(15nm)/Nb(10nm) heterostructured materials were prepared by DC Magnetron Sputtering and systematically studied by X-ray, magnetization and ferromagnetic resonance techniques. For thinner Nb buffer layer (≤10nm), it was found that there is an inter-diffusion at Co/IrMn interface, which favors double-like hysteresis loop. For thicker Nb layers, however, a gradual transition from double to single-like hysteresis loops is observed and it is associated with the reduction of the Nb roughness, which also enhances the exchange coupling at the Co/IrMn interface. Nb grown on IrMn layer induces the formation of an NbIrMn alloy layer, while no evidence of inter-diffusion at the Co/Nb interface is observed. For rougher Nb buffer layers (tNb