University of Minnesota
School of Physics & Astronomy
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Oriol T. Valls

Charge and spin currents in ferromagnetic Josephson junctions
K. Halterman, O.T. Valls, C-T Wu, Phys. Rev. B 92 174516 (2015)

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We determine, using a self consistent method, the charge and spin currents in ballistic Josephson junctions consisting of ferromagnetic (F) layers sandwiched between superconducting (S) electrodes (SFS-type junctions). When there are two F layers, we also consider the experimentally relevant configuration where a normal (N) nonmagnetic spacer layer separates them. We study the current-phase relationships as functions of geometrical parameters that are accessible experimentally including the angles that characterize the relative orientation of the magnetization in the F layers. Our self-consistent method ensures that the proper charge conservation laws are satisfied. As we vary the phase difference Δφ between the two outer S electrodes, multiple harmonics in the current phase relations emerge, their extent depends on the interface scattering strength and the relative F layer widths and magnetization orientations. By manipulating the relative F layer magnetization orientations, we find that the charge supercurrent can reverse directions or vanish altogether. These findings are discussed in the context of the generation and long-range nature of triplet pair correlation. We also investigate the spin currents and associated spin transfer torques throughout the junction. For noncollinear relative magnetizations, the non-conserved spin currents in a given F region gives rise to net torques that can switch directions at particular magnetic configurations or Δφ values. The details of the spin current behavior are shown to depend strongly on the degree of magnetic inhomogeneity in the system.