Increase Of Gilbert Damping In Permalloy Thin Films Due To Heat-Induced Structural Changes

Spin-wave based computing requires materials with low Gilbert damping, such as Ni80Fe20 (Permalloy) or yttrium iron garnet, in order to allow for spin-wave propagation on a length scale comparable to the device size. Many devices, especially those that rely on spin-orbit effects for operation, are subject to intense Joule heating, which can exacerbate electromigration and induce local phase changes. Here, the effect of annealing on the Gilbert damping coefficientalpha of 36nm Py thin films grown on a Si substrate is examined. Ferromagnetic resonance measurements, high resolution transmission electron microscopy, as well as energy dispersive x-ray spectroscopy have been employed to determinealpha while also studying structural changes in the thin films. The Gilbert damping parameter was found to increase sixfold when annealed at 350degrees C, which was linked to the diffusion of Ni atoms into the Si substrate on a length scale of up to 50nm. The results demonstrate that magnonic devices have to be treated with caution when Joule heating occurs due to its detrimental effects on the magnonic properties, but the effect can potentially be exploited in the fabrication of magnonic devices by selectively modifying the magnonic damping locally.