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.