Measurement of spin memory lengths in PdNi and PdFe ferromagnetic alloys

TL;DR

This study measures the spin memory lengths in PdNi and PdFe ferromagnetic alloys at 4.2 K using giant magnetoresistance in hybrid spin valves, providing key parameters for superconducting/ferromagnetic hybrid system research.

Contribution

First direct measurement of spin memory lengths in PdNi and PdFe alloys using current-perpendicular-to-plane GMR methods, aiding understanding of spin transport in ferromagnetic alloys.

Findings

Spin memory length in PdNi is approximately 2.8-5.4 nm.

Spin memory length in PdFe is approximately 9.6 nm.

PdFe has a longer spin memory length, consistent with lower spin-orbit scattering.

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.