Spin relaxation in multilayers with synthetic ferrimagnets

TL;DR

This paper investigates how the magnetic state of a synthetic ferrimagnet influences spin relaxation in a ferromagnetic layer, revealing tunable damping effects crucial for high-speed spintronic device design.

Contribution

It demonstrates the controllable modulation of spin relaxation in a ferromagnetic layer through the magnetic configuration of an interfaced synthetic ferrimagnet, depending on Cr spacer thickness.

Findings

Spin relaxation varies non-monotonically with Cr spacer thickness.

Magnetic state transitions from antiparallel to parallel affect spin damping.

Tunable spin relaxation can be achieved via magnetic configuration control.

Abstract

We demonstrate a strong tunability of the spin-pumping contribution to magnetic damping in a thin-film ferromagnetic free layer interfaced with a synthetic ferrimagnet (SFM), acting as a spin-sink, via a thin Cu-spacer. The effect strongly depends on the magnetic state of the SFM, a trilayer structure composed of two Fe layers coupled via indirect exchange mediated by a Cr spacer. With increasing Cr thickness, the SFM state undergoes a transition from an antiparallel via a non-collinear to a parallel configuration. We can explain the corresponding non-monotonous dependence of spin relaxation in the free layer in terms of a modulation of the longitudinal spin transport as well as relaxation of the transverse angular momentum in the SFM. The results should be useful for designing high-speed spintronic devices where tunability of spin relaxation is advantageous.