Magnetic-coupling-dependent spin-triplet supercurrents in helimagnet/ferromagnet Josephson junctions

TL;DR

This paper investigates how the magnetic structure of helimagnet/ferromagnet/helimagnet Josephson junctions influences the long-range spin-triplet supercurrents, revealing complex dependencies on layer thicknesses and magnetic coupling.

Contribution

The study provides a theoretical analysis of triplet supercurrent behavior in HM/F/HM Josephson junctions, highlighting non-monotonic dependence on layer thicknesses due to magnetic exchange coupling.

Findings

Supercurrent modulation depends on helimagnet layer thickness.

Maximum triplet supercurrent varies non-monotonically with layer thickness.

Magnetic exchange coupling influences supercurrent behavior.

Abstract

The experimental achievements during the past year in demonstrating the existence of long-ranged spin-triplet supercurrents in ferromagnets proximity coupled to singlet superconductors open up the possibility for new interesting physics and applications [for a review, see M. Eschrig, Phys. Today 64(1), 43 (2011)]. Our group reported the injection of triplet supercurrents into a magnetically uniform ferromagnet (Co) by sandwiching it between two helimagnet/superconductor (Ho/Nb) bilayers to form a Nb/Ho/Co/Ho/Nb-type Josephson device. In the function of the Ho layer thicknesses, the supercurrent was found to modulate in a complex way that seemed to depend on the magnetic structure of Ho. To understand this unusual behavior, we have theoretically studied the properties of an ideal Josephson device with a helimagnet/ferromagnet/helimagnet (HM/F/HM) barrier in the clean limit using the Eilenberger equation; we show, in particular, that the maximum triplet supercurrent that can pass across the barrier will depend non-monotonically on the thicknesses of the HM layers if the HM and F layers are magnetically exchange coupled at their interface.