Spin relaxation in Cu and Al spin conduits

Abstract

We study the spin relaxation in Al and Cu spin conduits embedded in non-local spin valve nanostructures. Measuring the key spin transport properties, we determine the spin and charge diffusion constants as well as the spin flip time. By varying the temperature, we find that the maximum of the nonlocal spin resistance change occurs at finite temperatures with a clear difference between Al and Cu. In particular, we find that the maximum of the non-local spin signal in Al is less pronounced and occurs at lower temperatures compared to Cu suggesting that the self-passivating Al surface plays a role. Having fabricated devices with both materials in identical processes, we can attribute the differences unambiguously to the differences in the spin current conduit materials properties rather than the fabrication process.

Accessing the fundamentals of magnetotransport in metals with terahertz probes

“…This model is well applicable for many metals, where the spin-flips for cold (that is, Fermi-level) sp-band electrons [8][9][10] (26) NiCoFe (26) NiCoFe (26) Cu (13) Cu (13) Cu (13) Cu (13) Cu (12) FM Figure 1 | Illustration of spin-dependent conduction in a spin valve, and the sample structure. a, Principle of the GMR e ect, based on spin asymmetry in electron scattering.…”

Spin currents injected electrically and thermally from highly spin polarized Co2MnSi

“…Such contributions have been largely overlooked in previous studies, where mostly spin relaxation mechanisms in the non-magnetic material are proposed to account for the temperature evolution of the signals, which are clearly not sufficient to explain our results. [20][21][22][23] A schematic depiction and a scanning electron microscope image of the patterned nanowires is shown in Figure 1. A 47 nm thick Co 2 MnSi and 42 nm thick Ag thin film is grown via rf sputtering and then nano-structured to obtain about 200 nm wide ferromagnetic electrodes with a 200 nm thick and 170 nm wide Cu nanowire on top by two-step lift-off electron beam lithography.…”

“…Whilst an obvious low temperature decrease in signal is not apparent in the recently studied Heusler non-local spin valves, 10,11 the occurrence of a maximum of the non-local signal at a certain temperature is well studied in literature. [20][21][22][23] The physical origin for this non monotonic behaviour is still an open question, with a variety of explanations having been put forward including surface scattering in the conduit, surface oxidation, grain boundaries, magnetic impurities and a manifestation of a Kondo effect. [20][21][22][23] To shed light onto the origin of the temperature dependence, we compare further below the electrically injected spin current to a thermally generated spin current.…”

“…[20][21][22][23] The physical origin for this non monotonic behaviour is still an open question, with a variety of explanations having been put forward including surface scattering in the conduit, surface oxidation, grain boundaries, magnetic impurities and a manifestation of a Kondo effect. [20][21][22][23] To shed light onto the origin of the temperature dependence, we compare further below the electrically injected spin current to a thermally generated spin current. If the temperature dependence is dominated by an effect of the spin current propagation in the spin current conduit, such as surface oxidation of the conduit, different injection methods should yield the same temperature dependence.…”

“…In both cases, the resulting signal depends both on the magnitude of the spin accumulation initially generated in the conduit and the decay of that spin accumulation as it approaches the detector. At higher temperatures, the spin relaxation in the conduit is expected to be dominated by the Elliott-Yafet spin relaxation mechanism, 30 since additional proposed contributions to spin relaxation such as surface scattering along the conduit length, 20,21,23 or the Kondo effect in the vicinity of the interface 22 are only expected to potentially play a role at low temperatures. In the Elliott-Yafet mechanism, the spin-flip scattering rate is proportional to the momentum scattering rate and therefore should scale with the resistivity of the conduit identically, regardless of the initial generation mechanism.…”