Spin Memory Loss Research Articles

Measurement of resistance and spin-memory loss (spin relaxation) at interfaces using sputtered current perpendicular-to-plane exchange-biased spin valves

We describe measurements using a technique for determining interfacial resistances and loss of spin-direction memory (spin relaxation) for nonmagnetic metals and nonmagnetic interfaces. The technique involves inserting the metal of interest, or a multilayer, into the middle of a current-perpendicular (CPP) permalloy-based exchange-biased spin-valve and monitoring the resulting increase in CPP resistance and decrease in magnetoresistance. The technique has the advantage over earlier ones of giving both uniform current and control of the required magnetic states. We test and validate the technique using (a) an alloy, CuPt (6 at. %), in which the spin-diffusion length has previously been measured with a different technique, (b) a metal, Ag, where we expect a long spin-diffusion length, and (c) Cu/Ag interfaces, where we expect little if any spin-memory loss. We then use the technique to measure spin-memory-loss (the spin-diffusion length) at 4.2 K of the antiferromagnetic alloy FeMn, which is used for pinning the ferromagnetic layers in our spin-valves, and of sputtered single layers of V, Nb, and W preparatory to measuring interfacial resistance and interfacial spin-memory loss in sputtered $[\mathrm{C}\mathrm{u}/\mathrm{A}\mathrm{g}{]}_{N},$ $[\mathrm{C}\mathrm{u}/\mathrm{V}{]}_{N},$ $[\mathrm{C}\mathrm{u}/\mathrm{N}\mathrm{b}{]}_{N},$ and $[\mathrm{C}\mathrm{u}/\mathrm{W}{]}_{N}$ multilayers with N repeats. To our surprise, we discovered large interfacial spin-relaxation rates for V/Cu, Nb/Cu, and W/Cu interfaces. These rates seem to be understandable as due to spin-orbit coupling in high resistivity interfacial alloys.

Enhancing current-perpendicular magnetoresistance in Permalloy-based exchange-biased spin valves by increasing spin-memory loss

Inserting a thin (t*=0.5 or 1 nm) layer of the antiferromagnet FeMn into the “free” Permalloy (Py) layer of a sputtered, current-perpendicular exchange-biased spin valve, Nb/FeMn/Py (pinned)/Cu/Py (free)/Nb, is shown to enhance AΔR, the difference in specific resistance between the states where the magnetizations of the two Py layers are parallel and antiparallel to each other. Such an increase is taken as evidence that spin-memory loss (spin relaxation) due to the FeMn is strong, and that judicious insertion of a source of spin relaxation into a multilayer with high specific resistance contacts can enhance AΔR, the numerator of the magnetoresistance.

Variation of multilayer magnetoresistance with ferromagnetic layer sequence: Spin-memory loss effects

We find the magnetoresistance (MR) with current flow perpendicular to the layer planes (CPP-MR) of multilayers made of the ferromagnetic metals Co and Py (permalloy=Ni84Fe16) and the nonmagnetic metal Ag to vary with the Co and Py layer sequencing. That is, [Co/Ag/Py/Ag]N (type I) multilayers have larger MRs than [Co/Ag]N[Py/Ag]N (type II) ones, and the difference grows with the number of repeats N. We ascribe the differences to an apparent short spin-diffusion length in Py. Interestingly, similar differences appear also in the current in plane MR, probably due to finite mean-free paths in all three metals, plus interface scattering.

Spin coupling and memory effects in the optical cycle of FH centers involving electron-vibrational energy transfer

Spin-coupling and spin memory effects of FH(OH−) and FH(CN-) centers have been studied in various hosts at 2 K. The spin-memory loss ϵ, i.e. the probability of spin-flip during a complete electronic excitation and relaxation cycle, has been determined. The main result is a strong increase of the spin-memory loss ϵ for FH(CN-) in CsCl and CsBr compared to F centers, while ϵ remains nearly unchanged (only a slight decrease) for FH(OH-) centers in KCl and KBr. First attempts will be made to explain these spin-memory loss results in correlation to the electron relaxation and electron-vibrational energy transfer processes occuring in the same optical cycle.

Spin-memory loss in optical cycle of F center

The spin-memory loss in optical pumping cycle of F center was found to be considerably large. Most part of spin-memory was lost in the non-radiative decay (NR) process. The spin-mixing parameters in optical absorption as well as NR process were determined from curve-fitting analysis of magnetic circular polarization of F center luminescence (Δ) versus the modulation frequency of circular polarization of pumping light, using a proportionality constant between Δ and the polarization difference in spin levels in the relaxed excited state of F center.