Superconducting Spin Valve Effect of a V Layer Coupled to an Antiferromagnetic $[\mathrm{Fe}/\mathrm{V}]$ Superlattice

We studied superconducting V layers deposited on an antiferromagnetically coupled $[{\mathrm{Fe}}_2{\mathrm{V}}_{11}{]}_{20}$ superlattice. The parallel upper critical magnetic field exhibits an anomalous $T$ dependence up to the ferromagnetic saturation field of the superlattice, indicating that the superconducting transition temperature $T_S$ decreases when rotating the relative sublattice magnetization directions of the superlattice from antiparallel to parallel. This proves that the pair breaking effect of a ${\mathrm{Fe}}_2$ layer is reduced if at a distance of 1.5 nm a second ${\mathrm{Fe}}_2$ layer with antiparallel spin orientation exists.

Figure 1

Magnetic hysteresis loop of the sample $[{\mathrm{Fe}}_2{\mathrm{V}}_{11}{]}_{20}/\mathrm{V}(18\mathrm{nm})$ measured at 10 K.

Figure 2

Upper critical magnetic field versus temperature with the field applied parallel and perpendicular to the film plane for three samples $[{\mathrm{Fe}}_2{\mathrm{V}}_{11}{]}_{20}/\mathrm{V}(d_V)$ from Table . The thickness $d_V$ is given in the figure, the open symbols refer to the magnetic field direction parallel to the film plane, the solid symbols refer to the direction perpendicular to the plane.

Figure 3

Square of the parallel upper critical magnetic field versus temperature for the sample $[{\mathrm{Fe}}_2{\mathrm{V}}_{11}{]}_{20}/\mathrm{V}(16\mathrm{nm})$ (a) and $[{\mathrm{Fe}}_2{\mathrm{V}}_{11}{]}_{20}/\mathrm{V}(30\mathrm{nm})$ (b). The solid straight line is the extrapolation of the linear temperature dependence for higher fields, and the dashed line is the theoretical curve expected if the magnetization of the superlattice does not change. $\Delta T_S$ is the shift of the superconducting transition temperature between the superlattice in the antiferromagnetic state and in ferromagnetic saturation. The inset in panel (a) depicts the shift of the superconducting transition temperature with the magnetization of the $[{\mathrm{Fe}}_2{\mathrm{V}}_{11}{]}_{20}$ superlattice.