COUPLING OF NI AND NIFE FILMS THROUGH AN INTERVENING NONMAGNETIC FILM

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/SiO2/NiFe/SiO2 sequence with the SiO2 films spanning the same thickness range as the Ag in the first sequence. It is believed that the coupling in Ni/Ag/NiFe is dominated by conduction-electron-spin polarization. Some of the coupling may be magnetostatic in origin.