We study the critical temperature T_c of SFF trilayers (S is a singlet superconductor, F is a ferromagnetic metal), where the long-range triplet superconducting component is generated at noncollinear magnetizations of the F layers. We demonstrate that T_c can be a nonmonotonic function of the angle \alpha between the magnetizations of the two F layers. The minimum is achieved at an intermediate \alpha, lying between the parallel (P, \alpha=0) and antiparallel (AP, \alpha=\pi) cases. This implies a possibility of a "triplet" spin-valve effect: at temperatures above the minimum T_c^{Tr} but below T_c^{P} and T_c^{AP}, the system is superconducting only in the vicinity of the collinear orientations. At certain parameters, we predict a reentrant T_c(\alpha) behavior. At the same time, considering only the P and AP orientations, we find that both the "standard" (T_c^{P} < T_c^{AP}) and "inverse" (T_c^{P} > T_c^{AP}) switching effects are possible depending on parameters of the system.Comment: 5 pages (including 4 EPS figures

We have investigated the differential resistance of hybrid planar Al-(Cu/Fe)-Al submicron bridges at low temperatures and in weak magnetic fields. The structure consists of a Cu/Fe bilayer forming a bridge between two superconducting Al electrodes. In the superconducting state of Al electrodes, we have observed a double-peak peculiarity in differential resistance of the S-(N/F)-S structures at a bias voltage corresponding to the minigap. We claim that this effect (the splitting of the minigap) is due to an electron spin polarization in the normal metal which is induced by the ferromagnet. We have demonstrated that the double-peak peculiarity is converted to a single peak at a coercive applied field corresponding to zero magnetization of the Fe layer.

We demonstrate that Josephson devices with nontrivial phase difference 0 < ϕ g < π in the ground state can be realized in structures composed from longitudinally oriented normal metal (N) and ferromagnet (F) films in the weak link region. Oscillatory coupling across F-layer makes the first harmonic in the current-phase relation relatively small, while coupling across N-layer provides negative sign of the second harmonic. To derive quantitative criteria for a ϕ-junction, we have solved two-dimensional boundary-value problem in the frame of Usadel equations for overlap and ramp geometries of S-NF-S structures. Our numerical estimates show that ϕ-junctions can be fabricated using up-to-date technology.

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The critical current I C of superconductor/ferromagnet-normal/superconductor ͑S/FN/S͒ Josephson junctions is calculated in the framework of linearized Usadel equations. The dependence of I C on the distance L between superconductors and thicknesses d F,N of ferromagnetic and normal layers is analyzed. It is shown that I C ͑L , d F ͒ may exhibit damping oscillations as a function of both arguments. The conditions have been determined under which the decay length and period of oscillation of I C ͑L͒ at fixed d F are on the order of decay length of superconducting correlations in the N metal, N , that is much larger than in F film. We demonstrate also that the positions of the points L = L n , at which I C = 0 exhibit damping oscillations as a function of d F . The number of transitions from 0 to states in I C ͑L , d F ͒ increases under L → L n . Outside these narrow intervals of L around L n sign and value of I C are independent on d F for d F տ F .

The critical currents I C of SNF-FN-FNS, SN-FN-NS, and SNF-N-FNS Josephson junctions ͑Ssuperconductor, F-ferromagnetic, N-normal metal͒ with complex SNF or SN electrodes ͑N or NF bilayer are situated under a superconductor͒ are calculated in the framework of linearized Usadel equations for arbitrary overlap length d of SN interface. We demonstrate that in these geometries, in the case of large resistances of SN interfaces, the critical current can exceed that in ramp-type junctions. Based on these results, the choice of the most practically applicable geometry is discussed. We predict that in a certain parameter range there is single 0-transition with the increase in the overlap length d. This single transition can be realized also in SFN-N-FNS Josephson junctions, where the coherence length in the weak-link region is a real quantity. Further, we predict that in SNF-N-FNS Josephson junctions 0-transition may take place with increase in distance between superconducting electrodes.