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Paper   IPM / Physic / 15466
School of Physics
  Title:   Spin transfer torque and exchange coupling in Josephson junctions with ferromagnetic superconductor reservoirs
  Author(s): 
1.  Z. Shomali
2.  R. Asgari
  Status:   Published
  Journal: J. Physics: Condens. Matter
  No.:  3
  Vol.:  32
  Year:  2019
  Pages:   035806
  Supported by:  IPM
  Abstract:
In this paper, the spin transfer torque (STT) and the exchange coupling of the Josephson junctions containing the interesting cases of diffusive/ballistic-triplet/singlet ferromagnetic superconductor (FS) materials together with the diffusive Josephson junction of the form S1/F1/I1/N/I2/F2 with I being the insulating barrier are investigated. Using the Nazarov quantum circuit theory, it is found that for the diffusive FS1/N/FS2 structure the STT only appears in the normal direction to the plane of the exchange fields of the F1 and F2. This results in the antiparallel/parallel or vice versa parallel/antiparallel transition of the favorable exchange coupling depending on the considered parameters of the system, including the nonmagnetic spacer thickness, the superconducting phase difference, the length and the exchange field of the ferromagnets. Furthermore, the analyze of the width of the transitions, the phase difference interval in which an interlayer length-induced antiparallel/parallel transition can be occurred, is performed. For instance, as the exchange field or the temperature increases, the interval of phase difference gets larger. On the other hand, the ballistic Josephson junction containing the triplet ferromagnetic superconductor reservoirs solving the 16×16 Bogoliubov-de-Gennes equation is studied. It is found that although the exchange fields of the FS are laid in the z and y direction, the STT interestingly exists in all three directions of x, y and z. This exciting finding suggests that the favorable equilibrium configuration concerning the least exchange coupling occurs in the relative exchange field direction different from 0 or π. To the best of our knowledge it is for the first time that the occurrence of the in-plane STT is reported. Moreover, the occurrence of the beat like behavior with two oscillation period for the out-of-plane STT is interestingly acquired.

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