Inter-magnet pumping counters dissipation in artificial ferrimagnets

Generating a spin current naturally increases the magnetic dissipation of its source, and this unavoidable rise in dissipation presents a substantial obstacle to achieving high-efficiency and low-loss spintronics applications. Despite substantial efforts to reduce dissipation, its positive correlation with spin current output remains an insurmountable barrier. Here we demonstrate a counterintuitive phenomenon: the effective damping of an artificial ferrimagnet, which quantifies the dissipation in its dynamics, is negatively correlated with the spin current output. In other words, higher output equals lower dissipation. To explain this unexpected result, we propose a complex mechanism in which inter-magnet pumping can counter dissipation in the presence of spin current output, transforming the usual increase in dissipation into a decrease. Along with this, we observe an improvement in spin current output efficiency, quantified through the effective spin-mixing conductance. These findings revise the current understanding of spin dynamics and could provide insights useful for developing high-efficiency, low-loss spintronic devices.