Speaker
Description
A thorough understanding of magnetic damping in ferromagnetic materials is of importance in spintronics from both a fundamental and a practical point of view. The phenomenological Gilbert parameter α in the Landau-Lifshitz equation is central to quantify the magnetic damping, which can be measured with ferromagnetic resonance (FMR). Permalloy (Py = Ni$_{80}$Fe$_{20}$) is one of the model systems with low magnetic damping. Here, we report the outcome of a systematic study of the temperature and frequency dependence of the FMR linewidth of Py, which was grown on typical substrates (silicon and sapphire) and capped with materials commonly used for preventing oxidation (Ta, Al, and SiOx). The resulting frequency and temperature dependence of the FMR linewidth deviates significantly from the expected Gilbert-like behavior. Unwanted non-Gilbert-like contributions appear, especially at low temperatures, and particularly for oxidic interfaces [1]. In contrast, metallic capping layers avoid non-Gilbert-like contributions. Special focus was paid to the influence of the Al spacer thickness which was varied between 1 and 10 nm [2]. In particular, Py sandwiched in between a metallic Al cap and a thin spacer layer exhibits negligible inhomogeneous FMR linewidth broadening and a very small, purely Gilbert-like contribution of α = 0.0068(2) down to the lowest temperature for a fixed Py layer thickness of nominally 20 nm [2]. In addition, the Gilbert damping parameter 𝛼 was studied as a function of Py layer thickness for Al-sandwiched Py thin films. The full FMR dataset allows to separate the Gilbert-like contributions to the FMR linewidth from non-Gilbert-like ones like two magnon scattering processes for the entire thickness series from 3 nm to 37 nm. We can deconvolute 𝛼 into its respective bulk and interfacial contributions and their respective temperature dependencies. While the bulk contribution monotonously decreases with temperature from 0.0061(1) down to 0.0054(1), and is thus of purely resistivitylike character [3]. In contrast, the interfacial contribution shows a subsequent increase at low temperature, i.e. it contains both resistivity and conductivity-like contributions [3]. The isolated bulk contribution, which is only of resistivity-like character, can be considered to reflect the intrinsic magnetic damping properties of Py thin films.
References
[1] V. Ney et al. Phys. Rev. Materials 7, 124403 (2023)
[2] V. Ney et al. Phys. Rev. Materials 8, 124410 (2024)
[3] V. Ney et al. Phys. Rev. Materials 10, 024409 (2026)