Damping and ferromagnetic resonance linewidth broadening in nanocrystalline soft ferromagnetic Fe-Co-Hf-N films

In order to describe high-frequency damping mechanisms of ferromagnetic films by means of the imaginary part of the frequency-dependant permeability, CMOS compatible ferromagnetic Fe(36)Co(44)Hf(9)N(11) films were deposited by reactive r.f.magnetron sputtering on oxidised 5 x 5 mm(2) x 380 mm ( 1 0 0)-silicon substrates with a 6-in. Fe(38)Co(47)Hf(15) target, as well as magnetic field annealing between 300 and 600 degrees C. An in-plane uniaxial anisotropy of around 4.5mT as well as an excellent soft magnetic behaviour with a saturation polarisation of approximately 1.4T could be observed after heat treatment at the above-mentioned temperatures, which drives these films to a high-frequency suitability. Ferromagnetic resonance frequencies of approximately up to 2.4GHz could be obtained. The frequency-dependant permeability was measured with a broadband permeameter. Depending on the heat treatment, an increase of the full-width at half-maximum (FWHM) of the imaginary part of the frequency-dependant permeability is discussed in terms of two-magnon scattering, anisotropy-type competition and local resonance generation through predominant grain growth causing magnetisation and anisotropy inhomogeneities in the magnetic films. The grain size of the films was determined by (HRTEM) imaging and amounts from a few nanometres for films heat treated at 300 degrees C to more than 10nm at 600 degrees C where the FWHM Delta f(eff) and the Landau - Lifschitz - Gilbert equation damping parameter alpha(eff) increases with d(nm)(2) and d(nm) ( e. g. dnm is the grain diameter of the nonmagnetic Hf-N phase), respectively. (C) 2008 Elsevier B. V. All rights reserved.