Annealing effect of sputter-grown Pt/Ni80Fe20/Pt sandwich trilayer films on Gilbert damping

Abstract

The annealing effect of Pt/Permalloy(Py: Ni80Fe20)/Pt sandwich trilayer films on Gilbert damping was investigated through ferromagnetic resonance, x-ray diffraction (XRD), and transmission electron microscopy (TEM) measurements. We estimated the variation of the effective Gilbert damping constant with 30-min-post-annealing temperature in the range of Ta = 600–800 K. The damping constant for the as-grown sample was estimated to be αeff = 0.021, but it linearly increased with Ta until 700 K and then drastically increased by 4.5 times up to αeff = 0.093 at Ta = 800 K. Delicate analyses of the XRD and TEM data revealed that the damping constant in such a thin-layered structure is closely related to the structural characteristics of the interfaces and atomic intermixing through them. The linear increase in αeff in the range of Ta = 650–700 K was ascribed to the alloying/intermixing effect between the Pt and Py layers through both interfaces, whose effect was found to be related to the degradation of the Pt (111) texture. Meanwhile, in the range of Ta = 750–800 K, αeff further and rapidly increased relative to the values in the range of Ta = 650–700 K. Specifically, the 800-K-post-annealed sample showed that its damping constant was 4.5 times larger than that of the as-grown sample, its saturation magnetization decreased by ∼54%, and also that new stoichiometric compounds such as NiPt, FePt, and NiFePt appeared. TEM equipped with energy-dispersive x-ray spectroscopy also revealed that Ta gives rise to atomic intermixing between the Pt and Py thin layers through both interfaces, resulting in interface shifting. This work provides the means to control the Gilbert damping constant and better to understand complex multi-layered structures in potential spintronic devices.