• Abstract:  Ferromagnetic resonance has been used to study the magnetic properties and magnetization dynamics of polycrystalline Fe_1-xV_x alloy films with 0 ≤ x < 0.7. Films were produced by co-sputtering from separate Fe and V targets, leading to a composition gradient across a Si substrate. FMR studies were conducted at room temperature with a broadband coplanar waveguide at frequencies up to 50 GHz using the flip-chip method. The effective demagnetization field 4pM_eff and the Gilbert damping parameter G have been determined as a function of V concentration. The results are compared to those of epitaxial FeV fims.

• Abstract:  Magnetization dynamics in confined systems is a topic of great current interest. It has recently become possible to study magnetic excitations in individual nanomagnets using ferromagnetic resonance (FMR), generated by a spin-torque (ST) interaction [1]. Here we report on a comparison of conventional broadband FMR on extended thin films with ST FMR excitation of the same films patterned down to 50 nm scale lateral dimensions using electron beam lithography. Experiments are conducted on || [xCo - 2[x Ni] × Ν | 10nm Cu | 12 nm Co|| structures, where x is the thickness of the Co layer. Varying x is shown to enable variation of the easy-plane anisotropy. Samples with x = 0.1, 0.2, 0.3 and 0.4 nm have been studied, where the number of bilayers is varied to keep the film thickness and total magnetic moment constant (N =1.2/x, x in nm). The samples were grown on Si-SiO₂ substrate by evaporation in UHV. Field sweep FMR measurements on extended films and nanopillar devices were conducted in a broad frequency range in the GHz regime (1 to 20 GHz). FMR studies of the thin films were carried out using a coplanar waveguide and the flip-chip method. The resonance field H_res and the linewidth ΔH were studied as a function of frequency for field-in plane and field perpendicular to the plane, and as a function of the field angle at constant frequency. The 2^nd and 4^th order perpendicular anisotropy constants were determined, as well as the magnetic damping parameter, α. ST FMR studies were conducted in the field perpendicular to the plane geometry. The frequency dependence of H_res and ΔH for the nanopillars is compared to that of the extended films. [1] J. C. Sankey et al., Phys. Rev. Lett. 96, 227601 (2006)

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• Abstract:  We present room temperature ferromagnetic resonance (FMR) studies of polycrystalline ||Pt/10 nm Cu/t Co/10 nm Cu/Pt|| films as a function of Co layer thickness (1 £ t £ 10 nm) grown by evaporation and magnetron sputtering. FMR was studied with a high frequency broadband coplanar waveguide (up to 25 GHz) using a flip-chip method. The resonance field and the linewidth were measured as a function of the ferromagnetic layer thickness. The evaporated films exhibit a lower magnetization density (M_s = 1131 emu/cm³) compared to the sputtered films (M_s= 1333 emu/cm³), with practically equal perpendicular surface anisotropy (K_s ~ -0.5 erg/cm²). For both series of films, a strong increase of the linewidth was observed for Co layer thickness below 3 nm. For films with a ferromagnetic layer thinner than 4 nm, the damping of the sputtered films is larger than that of the evaporated films. The thickness dependence of the linewidth can be understood in term of the spin pumping effect, from which the interface spin mixing conductance (g^?? S^-1) is deduced.

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