  Magnetic inhomogeneity at a superconductor (S)/ferromagnet (F) interface
converts spin-singlet Cooper pairs into spin-one triplet pairs. These pairs are
immune to the pair-breaking exchange field in F and support a long-range
proximity effect. Although recent experiments have confirmed the existence of
spin-polarised triplet supercurrents in S-F-S Josephson junctions, reversible
control of the supercurrent has been impossible because of the robust
pre-configured nature of the inhomogeneity. Here we use a barrier comprising
three F layers whose relative magnetic orientation, and hence the interfacial
inhomogeneity, can be controlled by small magnetic fields; we show that this
enables full control of the triplet supercurrent and, by using finite element
micromagnetic simulations, we can directly relate the experimental data to the
theoretical models which provide a general framework to understand the role
played by magnetic states in long-range supercurrent modulation.
