Ferromagnetic resonance in a coupled two-layer system

The microstructure and magnetic properties of polycrystalline Fe films with thicknesses of 200–1000 A have been investigated. The films were prepared by rf sputtering onto SiO2 substrates. The investigation was prompted by the lack of data on sputtered Fe films in this thickness regime as well as disagreement in the data for evaporated films. In addition to thickness, substrate temperature and deposition pressure were varied to examine their effect on the microstructure. The film microstructure was characterized by x‐ray diffraction, transmission electron microscopy, and Auger spectroscopy. The polycrystalline films did not display a strong preferred orientation and had average grain sizes of 60–85 A. Surface oxide layers formed upon exposure to air ranged from 10 to 80 A, the thicker oxides formed on films with lower density. Magnetic hysteresis measurements were made with a vibrating sample magnetometer. Below 1000 A, porosity and surface oxidation result in reductions up to 25% in the saturation magnet...

Magnetic properties of sputtered Fe thin films: Processing and thickness dependence

FMR properties of epitaxial Fe3O4 films on MgO(100)

Simulated spin wave resonance (SWR) lines on magnetic thin films have been studied by using a surface anisotropy field together with a surface inhomogeneity model for magnetization near the film surface. Landau-Lifshitz dynamic equations of motion of magnetization with Bloch-type damping have been used in order to obtain absorption lines as function of a steady magnetic field applied along a general direction with respect to the film surface. It has been found that the line shape, the resonance field values and especially the peak intensities for higher order spin wave modes strictly depend on the surface parameter. As the applied field direction is varied from perpendicular to parallel to the film plane, surface spin wave modes appear (or disappear) depending on easy (or hard) plane uniaxial surface anisotropy. The line width changes with field direction and has its maximum value at the angle corresponding to a rapid change of resonance fields, even for a constant intrinsic relaxation parameter used in the calculations. This anomalous broadening arises from a relatively slower increase of the effective internal resonance field due to dynamic response of steady magnetization to the increase of the applied fields during the resonance for any particular mode at these intermediate angles. Using this simulation, SWR spectra of a NiMn film on quartz substrate has been analyzed. The spectra comprise two surface modes in addition to the bulk modes when the angle between applied field and film normal is smaller than 45 degrees. From the angular variation of the SWR spectra, it is concluded that the surface spin pinning is mainly caused by an easy-plane uniaxial surface anisotropy field rather than surface inhomogeneity of the magnetization.

Simulated spin wave resonance absorption curves for ferromagnetic thin films and application to NiMn films

Spin-wave resonance and magnetic anisotropy in FePt thin films

We have used ferromagnetic resonance (FMR) at 33 GHz to study the properties of a number of evaporated thin Fe film systems. Values for effective anisotropy field HKeff , g value, and exchange constant A were derived. For Fe on glass, ‖HKeff ‖ was found to increase with increasing thickness. These changes were attributed to stress which decreased with film thickness. The presence of a Cu or a Ti underlayer did not seem to affect HKeff for films grown at room temperature. However, Fe/Ti/glass films made at higher substrate temperatures, Ts, did show an increase in ‖HKeff ‖. The appearance of a spin‐wave mode in the Fe films enables us to compute the exchange constant A for Fe, A=(2.12±0.14)×10−6 ergs cm−1. The coupling between two thin Fe films through an intervening Cu layer was investigated. A model predicting the number and position of the peaks in the spectrum as a function of coupling is presented. From experiment it was observed that the coupling remains almost constant through the 50–5‐nm Cu thickne...

FMR in evaporated single and multilayer thin Fe films

The magnetic coupling of 20‐nm‐thick Ni and Ni78Fe22 films through intervening Ag film has been investigated by ferromagnetic resonance (FMR) at 33 GHz. Films were deposited by e‐beam evaporation on glass in the order glass/Ag/Ni/Ag/NiFe/Ag. The Ag over‐ and underlays were 20 nm thick; the central Ag‐film thickness was varied between 0 and 20 nm. The coupling of the two ferromagnetic films, A and B, through the interface is modeled by adding −KMA⋅MB to the free energy per unit area. The FMR‐mode positions are found from the solutions of a quadratic in K. Subsequently, FMR‐mode intensities and linewidths are computed. Input data for these calculations were obtained from observations made on uncoupled Ni and NiFe films. From in‐plane dc‐field date a variation of K was deduced with a coupling film thickness t of the form exp(−t/τ) with τ equal to 2.68 nm. Limited FMR data taken with the dc field normal to the specimen are consistent with a weak coupling, K∼t−0.83. Little coupling was found in a glass/SiO2/Ni...

C. L. Jensen

Papers

FMR in evaporated single and multilayer thin Fe films

Coupling of Ni and NiFe films through an intervening nonmagnetic film