Supercurrent in ferromagnetic Josephson junctions with heavy-metal interlayers. II. Canted magnetization

Abstract

It has been suggested by theoretical works that equal-spin triplet pair correlations can be generated in Josephson junctions containing both a ferromagnet and a source of spin-orbit coupling. Our recent experimental work suggested that such triplet correlations were not generated by a Pt spin-orbit coupling layer when the ferromagnetic weak link had entirely in-plane anisotropy (N. Satchell and N.O. Birge, Phys. Rev. B 97, 214509 (2018)). Here, we revisit the experiment using Pt again as a source for spin-orbit coupling and a [Co(0.4 nm)/Ni(0.4 nm)]×8/Co(0.4 nm) ferromagnetic weak link with both in-plane and out-of-plane magnetization components (canted magnetization). The canted magnetization more closely matches theoretical predictions than our previous experimental work. Our results suggest that there is no supercurrent contribution in our junctions from equal-spin triplet pair correlations. In addition, this work includes the first systematic study of supercurrent dependence on Cu interlayer thickness, a common additional layer used to buffer the growth of the ferromagnet and which for Co may significantly improve the growth morphology. We report that the supercurrent in the [Co(0.4 nm)/Ni(0.4 nm)]×8/Co(0.4 nm) ferromagnetic weak links can be enhanced by over two orders of magnitude by tuning the Cu interlayer thickness. This result has important application in superconducting spintronics, where large critical currents are desirable for devices.

Boosting spintronics with superconductivity

“…75,76 We also note that vertical heterostructures with in-plane magnetization and ISOC interaction have been experimentally explored, but LRTC due to ISOC have not been observed. 77,78 Based on previous theoretical works, 73 the conditions for the generation of LRTC by SOC are quite restrictive in vertical structures, more favourable layouts are involving lateral structures where supercurrents have a component flowing in the direction parallel to the hybrid interfaces. 75,79…”

Odd triplet superconductivity induced by a moving condensate

“…Our proposal is based on the observation that the combination of exchange field, spin-orbit coupling (SOC), and controllable condensate motion is generically enough for the effective manipulation of the odd-frequency spin-triplet pairing states [2] which have attracted continual interest for several decades . We find that the condensate motion generated by the external magnetic field through the Meissner effect adds an additional degree of freedom which can control the generation of odd-frequency superconductivity in currently available experimental setups with SOC [28][29][30][31][32][33][34]. In the context of superconductor (S)/ferromagnet (F) hybrid structures [35][36][37][38][39][40][41][42][43][44] these correlations are known as long-range triplets (LRTs) because they can penetrate at large distances into the ferromagnetic material [9,[45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60].…”

Quasiclassical boundary conditions for spin-orbit coupled interfaces with spin-charge conversion

“…Several experiments have confirmed theoretical predictions in the case of hybrid structures comprised of superconductors and ferromagnets [14][15][16][17][18][19][20]. On the other hand, experimental studies of triplet superconductivity in hybrid structures of superconductors and spin-orbit coupled materials have started to appear mostly in recent years [26][27][28][29][30]. There exists several predictions [21][22][23][24][25] on emergent phenomena in structures combining superconducting and spin-orbit coupled materials * Both authors contributed equally to this work.…”