Ferromagnetic resonance of facing-target sputtered epitaxial γ′-Fe4N films: the influence of thickness and substrates

The microstructure and high frequency properties of facing-target sputtered epitaxial γ′-Fe4N films were investigated in detail. It was found that the eddy current in ultrathin γ′-Fe4N films is too small to influence the ferromagnetic resonance (FMR) linewidth, where the linewidth is mostly determined by intrinsic damping and the two-magnon scattering (TMS) process. In relatively thick films, the TMS process can significantly affect the linewidth due to the roughness on the sample surface. However, the TMS process in a thin film is quite weak because of its smooth surface. The Gilbert damping constant of about 0.0135 in our γ′-Fe4N films is smaller than the experimental value in the previous work. Moreover, substrates can also influence the FMR linewidth of the γ′-Fe4N films by the TMS process. Besides, the resonance field of polycrystalline γ′-Fe4N film is larger than the epitaxial ones because of the lack of a magnetic anisotropic field, but the linewidth of the polycrystalline γ′-Fe4N film is smaller.

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