Controlling supercurrents and their spatial distribution in ferromagnets

Spin-triplet Cooper pairs induced in ferromagnets are part of the field of superconducting spintronics. Triplet pairs can be generated in stacked ferromagnetic (F) layers between superconducting (S) contacts. In such stacks, spin-dependent scattering of a singlet in one layer generates a triplet m_S = 0 component, which, in the next ferromagnet with a different magnetization direction, manifest itself as an m_S = 1, or ‘equal-spin’ triplet. There are other configurations, however, to produce controllable triplet currents. Here we discuss two experiments based on a disk-shaped ferromagnetic layer as supercurrent carrier. The in-plane magnetization forms a vortex, with in the center a core where the magnetic flux is forced out. In one experiment, two S / F contacts generate a triplet supercurrent in the disk, and we show how the supercurrent can be controlled by moving the vortex with an in-plane magnetic field. In the other, we show that a triplet current can even be generated by placing S contacts directly on top of the disk, without the presence of the second ferromagnet. Again, the supercurrent is sensitive to the position of the magnetic vortex core. Apparently, the rotating magnetization, combined with the edges of the structure, yields the correct kind of inhomogeneity.