High Frequency Response of Magnetically Coupled Co/Cu/CoFeB Trilayers

Engineering the magnetic behaviour of stacks of ferromagnetic and non-magnetic thin films is mainly controlled by the anisotropy of individual layers plus the interlayer exchange coupling constant. In this context, Co/Cu/CoFeB trilayers with different Cu layer thicknesses were fabricated and the magnetization reversal processes, the interlayer coupling, the FMR frequencies and the damping parameters were studied. Their acoustic and optic modes, combined with their related damping parameters have been analyzed as a function of the Cu layer thickness. Particularly, the resonance frequency of the optic mode is very sensitive to the interlayer coupling constant that allows us to conclude that high resonance frequencies (i.e., above 25 GHz) can be achieved for ferromagnetically coupled bilayers with an interlayer exchange coupling like
${J}_{{eff}}=({2.7}\pm \mathbf{0.8})\ \mathbf{erg}/\mathbf{cm}^{\mathbf{2}}$
.