Large spin pumping effect in antisymmetric precession of Ni$_{79}$Fe$_{21}$/Ru/Ni$_{79}$Fe$_{21}$

TL;DR

This study demonstrates that antisymmetric precession modes in NiFe/Ru/NiFe trilayers produce a significantly larger spin pumping effect, doubling the Gilbert damping compared to symmetric modes, with implications for GHz spintronic devices.

Contribution

It provides experimental evidence that antisymmetric precession modes enhance spin pumping effects in magnetic trilayers, confirming theoretical predictions.

Findings

Antisymmetric mode shows twice the spin pumping effect of symmetric mode.

Gilbert damping increases by approximately 0.006 in antisymmetric mode.

Effect observed across multiple geometries and frequency ranges.

Abstract

In magnetic trilayer structures, a contribution to the Gilbert damping of ferromagnetic resonance arises from spin currents pumped from one layer to another. This contribution has been demonstrated for layers with weakly coupled, separated resonances, where magnetization dynamics are excited predominantly in one layer and the other layer acts as a spin sink. Here we show that trilayer structures in which magnetizations are excited simultaneously, antisymmetrically, show a spin-pumping effect roughly twice as large. The antisymmetric (optical) mode of antiferromagnetically coupled Ni$_{79}$Fe$_{21}$(8nm)/Ru/Ni$_{79}$Fe$_{21}$(8nm) trilayers shows a Gilbert damping constant greater than that of the symmetric (acoustic) mode by an amount as large as the intrinsic damping of Py ($\Delta \alpha\simeq\textrm{0.006}$). The effect is shown equally in field-normal and field-parallel to film plane geometries over 3-25 GHz. The results confirm a prediction of the spin pumping model and have implications for the use of synthetic antiferromagnets (SAF)-structures in GHz devices.