Broadband in-plane ferromagnetic resonance measurements were performed over a frequency range from 7 to 40 GHz on various Co56Fe24B20 systems with adjacent thin non-magnetic layers of Ru, Ta and Cu. Co56Fe24B20 samples bounded by either Ru or Ta layers exhibit a contribution to the Gilbert damping constant inversely proportional to the thickness of the Co56Fe24B20 layer, consistent with spin-pumping theory. In contrast, samples with 20 nm thick Cu bounding layers did not show a significant dependence of the Gilbert damping constant on the Co56Fe24B20 thickness, which can be understood based on the far larger spin diffusion length of Cu in comparison with Ru or Ta.
Ferromagnetic resonance and permeability linewidths of high-moment FeTiN thin films have been recorded and analyzed using ripple theory in order to separate inhomogeneous broadening from the intrinsic damping of the material. These results are compared to the analysis of the same phenomenon using a simple but common model of amplitude dispersion. The ripple is also used to analyze the behavior of the resonance frequency of a sample when rotated in low fields.
Thermally stable films of FeTiN, have been prepared and characterized by ferromagnetic resonance, x-ray diffraction, x-ray photoelecton spectroscopy, and magnetostriction measurements to determine the relationships between the microstructure and the damping constants. The resonance studies were carried out at multiple frequencies to determine the intrinsic damping constant, α, and the extrinsic damping constant, ΔH0, as well as values of the anisotropy field, Hk, the gyromagnetic ratio, γ, and the saturation magnetization value, 4πMs. Data from similar experiments on CoFe films were compared with the FeTiN data. Our results show no relationship between intrinsic damping and the magnetostriction, but a strong dependence of the extrinsic constant on the grain size.
The effect of interface roughness on exchange bias for NiFe/FeMn bilayers is investigated for polycrystalline films and epitaxial films. Three different systems were investigated: polycrystalline Ta (10 nm)/Ni80Fe20 (10nm)/Fe50Mn50 (20 nm) films on oxygen plasma-etched Si(100) or Cu/H–Si(100) and epitaxial Ni80Fe20 (10nm)/Fe60Mn40 (20 nm) films on Cu/H–Si(110). For films grown on plasma-etched substrates, as the etching time is increased, film roughness increases up to 12 nm. For the polycrystalline films grown on ultrathin Cu underlayers, x-ray diffraction shows the fcc (111) texture is greatly reduced as the thickness is increased. The epitaxial Cu/Si(110) buffer layer induces fcc (111) epitaxial growth and modifies the interface morphology. The dependence of exchange bias on roughness for each set of samples is explained in terms of a competition between the interfacial exchange coupling and the af uniaxial anisotropy.
The high frequency characteristics of 100 nm FeTaN films have been studied by using both time-resolved inductive techniques and frequency-resolved permeability measurements. Experiments performed as a function of longitudinal bias fields from 120 to 2400 A/m ͑1.5-30 Oe͒ showed precessional frequencies from 1.3 to 2.5 GHz, initial permeabilities from 1600 to 500, and damping constants ␣ϭ0.013 to 0.0045. It is illustrated that the magnetization precessional data obtained from the time-resolved inductive technique can be Fourier transformed to the frequency domain to give the real and imaginary components of a permeability spectrum; this spectrum compares well with data obtained from frequency-resolved permeability measurements. It is also demonstrated that accurate values of the damping constant ␣ can only be determined from permeameters whose bandwidth is two to three times the ferromagnetic resonance frequency of the material to be measured.
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