Enhancement of the Spin Pumping Effect by Magnon Confluence Process in YIG/Pt Bilayers

Abstract

The experimental investigation of the spin pumping process by dipolar‐exchange magnons parametrically excited in in‐plane magnetized yttrium iron garnet/platinum bilayers is presented. The electric voltage generated in the platinum layer via the inverse spin Hall effect (ISHE) results from contributions of two opposite spin currents formed by the longitudinal spin Seebeck effect and by the spin pumping from parametric magnons. In the field‐dependent measurements of the spin pumping‐induced component of the ISHE‐voltage, a clearly visible sharp peak is detected at high pumping powers. It is found that the peak position is determined by the process of confluence of two parametrically excited magnons into one magnon possessing twice the frequency and the sum of the wavevectors of the initial magnons. It is demonstrated that under the action of a rather strong parametric pumping field this confluence process results in the increase of the total number of magnons in the magnetic sample, and thus leads to the enhancement of the spin pumping effect.

Dependence of Nonlinear Response and Magnon Scattering on Damping

“…The critical amplitude b cr is linearly proportional to damping constant α, which demonstrates that the relaxation rate η k of k ࣔ 0 magnons is proportional to α. We also find that the threshold microwave power scales as α 4 . This sensitive scaling suggests a wide range for important nonlinear properties that is tunable through varying the damping constant α, such as by adding impurities to materials.…”

“…Examining its quantitative dependence of P th on α in Fig. 3(b), we find that P th scales as α 4 , and thus shows a very sensitive dependence on α. When α varies an order of magnitude, P th changes as 10 4 .…”

“…Nonlinear microwave devices based on magnons are of great interest, benefiting from low power consumption, simple implementation, and size miniaturization, all compared to their electrical counterparts [1]- [4]. This benefit arises from intrinsic physical characteristics of magnons, including long coherence length, extended lifetime and low energy dissipation [5], [6].…”

Directional Field-Dependence of Magnetoimpedance Effect on Integrated YIG/Pt-Stripline System

“…The second contribution to the effective damping parameter comes from the two-magnon and spin pumping mechanisms, especially due to the bilayer structure of our sample. There are numerous interesting studies playing with the mechanisms influencing and bringing the theoretical background to understand contributions for a given system [ 39 , 40 , 41 , 42 , 43 ]. Here, we do not address such issue in detail and instead focus our efforts in the fit using Equation ( 6 ) to infer the effective damping parameters and the extrinsic inhomogeneous contribution to .…”

Effect of magnon decays on parametrically pumped magnons

“…4 In the experiment 1 a thin YIG film was exposed to an oscillating magnetic field H(t) = H 0 e z + H 1 cos(ω 0 t)e z , where the static part H 0 e z forces the macroscopic magnetization to be aligned along the z-axis e z , while the oscillating part with amplitude H 1 H 0 drives the magnons in the sample out of equilibrium. Noack et al 1 observed that the spinpumping effect was enhanced for certain values of the static field H 0 , and that the magnon density in the stationary non-equilibrium state displayed peaks or dips for those values of H 0 where magnon decays due to the confluence of two parametrically excited magnons with identical energy and momentum becomes kinematically possible. Recall that magnon decays due to the confluence and the reverse splitting process conserve the total energy and momentum of the magnons involved in these scattering processes.…”