We analyze the dc Josephson effect in a ballistic superconductor/ferromagnet/superconductor junction by means of the Bogoliubov-de Gennes equations in the quasiclassical Andreev approximation. We consider the possibility of ferromagnetism originating from a mass renormalization of carriers of opposite spin, i.e. a spin bandwidth asymmetry. We provide a general formula for Andreev levels which is valid for arbitrary interface transparency, exchange interaction, and bandwidth asymmetry and analyze the current-phase relation, free energy, and critical current, in the short junction regime. We compare the phase diagrams and the critical current magnitudes of two identical junctions differing only in the mechanism by which the mid-layer becomes magnetic. We show that a larger number of 0 − π transitions caused by a change in junction width or polarization magnitude is expected when ferromagnetism is driven by spin bandwidth asymmetry compared to Stoner magnetism. Moreover, we show that these features can be present also for ferromagnets of the Stoner type having only a partial bandwidth asymmetry. PACS numbers: 74.50.+r,74.45.+c,72.25.-b,74.25.Dw arXiv:1012

We analyze the dc Josephson effect in a ballistic superconductor/half-metal/superconductor junction by means of the Bogoliubov-de Gennes equations. We study the role of spin-active interfaces and compare how different superconductor symmetries, including d-wave pairing, affect the Josephson current. We analyze the critical current as a function of junction width, temperature, and spin-flip strength and direction. In particular, we demonstrate that the temperature-dependence of the supercurrent in the dxy-symmetry case differs qualitatively from the s-and d x 2 −y 2 -symmetries. Moreover, we have derived a general analytical expression for the Andreev bound-state energies which shows how one can either induce 0−π-transitions or continuously change the ground state phase of the junction by controlling the magnetic misalignment at the interfaces.

We compute self-consistently the Josephson current in a superconductor-antiferromagnet-superconductor junction using a lattice model, focusing on 0 − π transitions occurring when the width of the antiferromagnetic region changes from an even to an odd number of lattice sites. Previous studies predicted 0 − π transitions when alternating between an even and an odd number of sites for sufficiently strong antiferromagnetic order. We study numerically the magnitude of the threshold value for this to occur, and also explain the physics behind its existence in terms of the phase-shifts picked up by the quasiparticles constituting the supercurrent in the antiferromagnet. Moreover, we show that this threshold value allows for pressure-induced 0 − π transitions by destroying the antiferromagnetic nesting properties of the Fermi surface, a phenomenon which has no counterpart in ferromagnetic Josephson junctions, offering a new way to tune the quantum ground state of a Josephson junction without the need of multiple samples. Introduction. The study of the interplay between superconductivity and magnetism has been of considerable interest in condensed matter physics over the last decades. Phenomena such as the 0 − π-transition 1 in ferromagnetic Josephson junctions has received much attention both from a fundamental quantum physics point of view in addition to being suggested as a potential basis for qubits. 2 . While most of the focus in the above context has been on ferromagnetic (F) order, antiferromagnetic (AF) Josephson junctions are also of fundamental interest, due to the close relationship between the superconducting (S) phase and the antiferromagnetic phase in for instance high-temperature cuprate and iron-pnictide superconductors. Superconductivity and antiferromagnetism spindensity wave states may even coexist in the superconducting pnictides. 3 Similar to SFS junctions, antiferromagnetic Josephson junctions (SAFS) have been predicted to display 0 − π-transitions 4 . However, for SAFS these transitions display a high sensitivity to the exact number of atomic layers (even vs. odd number) in the antiferromagnet. Ref. 5 reported that an antiferromagnetic Josephson junction is in a π-state for an odd number of layers, while it is in the 0-state for an even number of layers provided that the antiferromagnetic order is much stronger than the superconducting order. An evenodd effect has also been observed in Josephson junctions with magnetic impurities in the middle layer. 6 In this Rapid Communication, we report on a novel aspect of antiferromagnetic Josephson junctions which allows for control over 0 − π transitions within a single sample in a way which has no counterpart in SFS structures. We first compute numerically the threshold value for the antiferromagnetic order parameter at which the even-odd effect occurs. Below this threshold, even and odd junctions behave qualitatively similar, both displaying a monotonic decay of the supercurrent with superimposed small-scale oscillations, but without any sign-change of t...

It has recently been proposed that spin-transfer torques in magnetic systems with anisotropic exchange can be strongly enhanced, reducing the characteristic current density with up to four orders of magnitude compared to conventional setups. Motivated by this, we analytically solve the equations of motion in a collective-coordinate framework for this type of anisotropic exchange system, to investigate the domain wall dynamics in detail. In particular, we obtain analytical expressions for the maximum attainable domain wall velocity of such a setup and also for the occurrence of Walker breakdown. Surprisingly, we find that, in contrast to the standard case with domain wall motion driven by the non-adiabatic torque, the maximum velocity obtained via the anisotropic exchange torque is completely independent of the non-adiabaticity parameter β, in spite of the torque itself being very large for small β. Moreover, the Walker breakdown threshold has an opposite dependence on β in these two cases, i.e. for the anisotropic exchange torque scenario, the threshold value decreases monotonically with β. These findings are of importance to any practical application of the proposed giant spin-transfer torque in anisotropic exchange systems.

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