Determination of the Pt spin diffusion length by spin-pumping and spin Hall effect

Abstract

The spin diffusion length of Pt at room temperature and at 8 K is experimentally determined via spin pumping and spin Hall effect in permalloy/Pt bilayers. Voltages generated during excitation of ferromagnetic resonance from the inverse spin Hall effect and anisotropic magnetoresistance effect were investigated with a broadband approach. Varying the Pt layer thickness gives rise to an evolution of the voltage line shape due to the superposition of the above two effects. By studying the ratio of the two voltage components with the Pt layer thickness, the spin diffusion length of Pt can be directly extracted. We obtain a spin diffusion length of ∼1.2 nm at room temperature and ∼1.6 nm at 8 K.

All-electrical manipulation of magnetization dynamics in a ferromagnet by antiferromagnets with anisotropic spin Hall effects

“…The inverse of the prefactor, i.e., 2Re[G eff ↑↓ ]/(σ/λ), is introduced as the spin current 'transmissivity', T. According to Eq. (7), T is very sensitive to the spin diffusion length, which in itself is a material-dependent parameter that requires careful calibration for many spin Hall metals 22,[48][49][50][51][52][53] . Increasing the spin diffusion length linearly enhances the value of T and decreases the value of θ …”

Spin-scattering rates in metallic thin films measured by ferromagnetic resonance damping enhanced by spin-pumping

“…An outstanding question remains as to how spin-and charge-transport are related in high-Z metals such as Pt and Pd [25,26,27,28,29,30]. In the standard spincharge diffusion equations, spin-transport is dependent on the charge conductivity, as can be seen in the standard time-independent, steady-state equations that describe spin-diffusion [31,32,33,34,35], …”

Evidence for Dyakonov-Perel-like Spin Relaxation in Pt

“…Nevertheless, the values and the mechanisms controlling these parameters are still debated. In particular, the reported values of the spin Hall angle in Pt range from 0.004 to over 0.1 [10,14,23], and those of λ range from less than 1 nm to over 10 nm [10,14,18,[20][21][22][24][25][26]. Such a large spread of the reported characteristics makes it challenging to establish the dominant contributions to spin-orbit effects and the mechanisms controlling them.…”

“…A variety of approaches have been utilized to determine the parameters relevant to SOI in Pt such as the spin Hall angle and λ [10,14,18,[20][21][22]. Nevertheless, the values and the mechanisms controlling these parameters are still debated.…”