Variation of effective damping with temperature in permalloy/Gd heterostructures
Peng Zhang, Shuangfeng Li, J. Yao, Hanwen Zhang, Xiaoyu Feng, Qihan Zhang, Jiangwei Cao, Xiaolong Fan, Desheng Xue
Abstract
In this study, we systematically investigate the temperature dependence of effective damping in FeNi (permalloy or Py)/Gd bilayer based on broadband ferromagnetic resonance. Despite a significant increase in the effective damping of the Py/Gd bilayer with decreasing temperature, we show that the spin pumping is not responsible for the result. By combining our findings with systematic measurement data of Py/Cu/Gd contrast samples, we conclude that an effective damping enhancement from a decrease in temperature is due to the temperature-dependent magnetic moment of Gd and antiferromagnetic coupling between Py and Gd. Further, we perform a semiquantitative analysis of the experimental data using the Landau-Lifshitz-Gilbert equations that consider the antiferromagnetic coupling between Py and Gd, and estimated the damping parameters in the range of 0.3--0.4 for Gd films with thicknesses of 5 and 8 nm. Our results suggest that to analyze the spin transport in heterostructure with several magnetic layers, it is necessary to commence from the fundamentals of magnetization dynamics considering interlayer coupling and avoid the overuse of spin pumping.