Observation of the ‘inverse’ spin valve effect in a $\mathrm{Ni/V/Ni}$ trilayer system

An experimental study of magnetic and superconducting properties of a trilayer $\mathrm{Ni/V/Ni}$ thin film system grown on single-crystalline $\mathrm{MgO(001)}$ substrate is reported. The field dependence of the superconducting transition temperature $T_c$ for samples comprising Ni layers with similar values of the coercive field $H_c$ reveals no anomalies. However, in samples with different thicknesses of the nickel layers the difference in $H_c$ amounts up to $\Delta H_c\sim1.8$ kOe, thus enabling to manipulate the relative orientations of the layers' magnetization by an external magnetic field. Surprisingly, for these samples the $T_c$ for the parallel orientation of the magnetizations of the $\mathrm{Ni}$ layers is higher, in a certain magnetic field range, than for the antiparallel one, at odds with theoretical predictions. Possible reasons of this contradiction are discussed.