Josephson coupling through ferromagnetic heterojunctions with noncollinear magnetizations

Abstract

We study the Josephson effect in clean heterojunctions that consist of superconductors connected through two metallic ferromagnets with insulating interfaces. We solve the scattering problem based on the Bogoliubov-de Gennes equation for any relative orientation of in-plane magnetizations, arbitrary transparency of interfaces, and mismatch of Fermi wave vectors. Both spin singlet and triplet superconducting correlations are taken into account, and the Josephson current is calculated as a function of the ferromagnetic layers thicknesses and of the angle α between their magnetizations. We find that the critical Josephson current Ic is a monotonic function of α when the junction is far enough from 0 − π transitions. This holds when ferromagnets are relatively weak. For stronger ferromagnets, variation of α induces switching between 0 and π states and Ic(α) is non-monotonic function, displaying characteristic dips at the transitions. However, the non-monotonicity is the effect of a weaker influence of the exchange potential in the case of non-parallel magnetizations. No substantial impact of spin-triplet superconducting correlations on the Josephson current has been found in the clean limit. Experimental control of the critical current and 0−π transitions by varying the angle between magnetizations is suggested.

Spin-valve Josephson junctions for cryogenic memory

“…[20][21][22][23] This could be accomplished by using a "pseudo spin valve" consisting of a magnetically "hard" material for the fixed layer and a magnetically "soft" material for the free layer, so that the magnetization of the free layer can be reversed by a small magnetic field without disturbing the magnetization of the fixed layer. This creates two magnetic states when the layer magnetizations are parallel or antiparallel which can have different critical current or phase shift values.…”

Tunable 0-π transition by spin precession in Josephson junctions

“…It is thus natural to ask what would happen to the Josephson current when a spin transistor is connected with two superconductor leads. The study of Pajović et al 12 shows that a 0-transition is induced by varying the angle between the two FM moments in a S/FM/FM/S junction, which suggests RSOC can be used to tune 0-transitions electrically.…”

“…Then the ferromagnetic influence of two parallel FM layers perfectly cancels out just like in the case of antiparallel magnetizations in the S/FM/FM/S model. 12 As a result, the junction changes from a state to a 0 state. In Fig.…”

Theory of Josephson effect in junctions with complex ferromagnetic/normal metal weak link region

“…In the limit of thin F and N films d N ξ N , d F ξ F , the of solution of Usadel equations in the N film of weak link has more simple form compare to (6.45): 55) while in FN bilayer under S electrodes it closes to that of (6.49), and (6.50) The integration constants in (6.55), (6.56), (6.57) can be found from the boundary conditions. In particular for A 1 and A 2 one can get…”

“…The next class of SFS junctions exploits the idea of interplay between singlet and odd triplet superconducting components inside a Josephson structure [58], [60], [55]- [57].…”