Measurement of spin memory lengths in PdNi and PdFe ferromagnetic alloys

Abstract

Weakly ferromagnetic alloys are being used by several groups in the study of superconducting/ferromagnetic hybrid systems. Because spin-flip and spin-orbit scattering in such alloys disrupt the penetration of pair correlations into the ferromagnetic material, it is desirable to have a direct measurement of the spin memory length in such alloys. We have measured the spin memory length at 4.2 K in sputtered Pd0.88Ni0.12 and Pd0.987Fe0.013 alloys using methods based on current-perpendicular-to-plane giant magnetoresistance. The alloys are incorporated into hybrid spin valves of various types, and the spin memory length is determined by fits of the Valet-Fert spin-transport equations to data of magnetoresistance vs. alloy thickness. For the case of PdNi alloy, the resulting values of the spin memory length are lsf(PdNi) = 2.8 +/- 0.5 nm and 5.4 +/- 0.6 nm, depending on whether or not the PdNi is exchange biased by an adjacent Permalloy layer. For PdFe, the spin memory length is somewhat longer, lsf(PdFe) = 9.6 +/- 2 nm, consistent with earlier measurements indicating lower spin-orbit scattering in that material. Unfortunately, even the longer spin memory length in PdFe may not be long enough to facilitate observation of spin-triplet superconducting correlations predicted to occur in superconducting/ferromagnetic hybrid systems in the presence of magnetic inhomogeneity.Comment: 7 pages, 8 figure

Resonant Andreev Spectroscopy in normal-Metal/thin-Ferromagnet/Superconductor Device: Theory and Application

“…More interestingly, the remaining parameters involved in the fitting procedure take values in narrow intervals, 51.2 < r < 55.1 and 0.140 < h < 0.146, from which it is possible to give an estimation of the ferromagnet thickness 4.3 nm < d < 4.6 nm in the various sample positions and of the corresponding spin polarization 14.0% < P < 14.6%. This finding is compatible with polarization values already reported in literature 33 .…”

Observation of Spin-Triplet Superconductivity in Co-Based Josephson Junctions

“…We believe that the decrease in I c R N at large d X , visible for X = PdNi, is caused by the destruction of the spintriplet correlations created at the Nb/Cu/X interface due to spin memory loss in the bulk of the X layers. The spin memory lengths in these PdNi and CuNi alloys are very short -about 2.8 nm in PdNi [13] and 1.4 nm in CuNi [14]. This would explain why we found no evidence for spin-triplet supercurrent in our previous measurements of Josephson junctions containing only PdNi layers of thickness 30-100 nm [11].…”

“…Presumably the domain structure of the PdNi is changed by exchange-coupling to the Co, in a way that is detrimental to production of the triplet correlations. We suspect that the PdNi magnetization is forced to lie in-plane near the interface with Co, which leads to less non-collinear magnetization in neighboring domains [13].…”

Spin-triplet supercurrent through inhomogeneous ferromagnetic trilayers

“…Due to the rich physics from a fundamental viewpoint and the possibility of birthing practical applications, configurations containing superconductors and ferromagnets have attracted much attention theoretically [4][5][6][7][8]11,12 and experimentally 1-3,9,10,13-15 over the last years (see for instance Ref. 2 for a comprehensive review and reference-list).…”