Exchange bias features in FeNi/FeMn/Gd-Co films

•Exchange bias in antiferromagnetic/ferrimagnetic layered system.•Magnetic compensation state for ferrimagnetic Gd-Co layer.•Sharp increase and inversion of the sign of exchange bias field for Gd-Co layer. The exchange bias effect in FeNi/FeMn/GdxCo100-x films with a pinning antiferromagnetic FeMn layer and an exchange-biased ferrimagnetic amorphous Gd-Co layer was studied. The FeNi layer allows the formation of the fcc lattice of FeMn, i.e. the antiferromagnetic γ-phase of FeMn. The Gd content was varied within 15–25 at. % in order to obtain different temperature dependences of the spontaneous magnetization Ms(T) of the Gd-Co layer. The magnetic properties of the films were determined from hysteresis loops measured in the temperature range 5–350 K. A correlation between Ms(T) and the temperature dependences of the exchange bias field HebGdCo(T) was established. In particular, it was shown that there is an inversion of the sign and sharp increase of the value of HebGdCo near the magnetic compensation state. The first one is a consequence of the minimization of the spontaneous magnetization of Gd-Co layer at the compensation temperature. The second one shows the predominance of the exchange interaction of the antiferromagnetic layer with the cobalt magnetic sub-system of the ferrimagnetic layer as a contribution to the interlayer exchange coupling.