Impedance of nanometer thickness ferromagnetic Co40Fe40B20 films

Nanocrystalline Co40Fe40B20 films, with film thickness t(f) = 100 nm, were deposited on glass substrates by the magnetron sputtering method at room temperature. During the film deposition period, a dc magnetic field, h = 40 Oe, was applied to introduce an easy axis for each film sample: one with h parallel to L and the other with h parallel to w, where L and w are the length and width of the film. Ferromagnetic resonance (FMR), ultrahigh frequency impedance (IM), dc electrical resistivity (rho), and magnetic hysteresis loops (MHL) of these films were studied. From the MHL and r measurements, we obtain saturation magnetization 4 pi M-s = 15.5 kG, anisotropy field H-k = 0.031 kG, and r = 168 mW.cm. From FMR, we can determine the Kittel mode ferromagnetic resonance (FMR-K) frequency f(FMRK) = 1,963 MHz. In the h parallel to L case, IM spectra show the quasi-Kittel-mode ferromagnetic resonance (QFMR-K) at f(0) and the Walker-mode ferromagnetic resonance (FMR-W) at f(n), where n = 1, 2, 3, and 4. In the h parallel to w case, IM spectra show QFMR-K at F-0 and FMR-W at F-n. We find that f(0) and F-0 are shifted from f(FMRK), respectively, and f(n) = F-n. The in-plane spin-wave resonances are responsible for those relative shifts. PACS No. 76.50.+q; 84.37.+q; 75.70.-i