Ferromagnetic Resonance Study of Fe/FePt Coupled Films With Perpendicular Anisotropy

We have studied exchange coupled FePt/Fe magnetic layers using the technique of ferromagnetic resonance (FMR). The FePt layers show strong uniaxial perpendicular anisotropy, growing in the L1₀ epitaxial phase on MgO (100). We have considered the case for two thicknesses of Fe: 2 nm and 3.5 nm, which exhibit rigid magnet and exchange-spring behavior. All FePt thicknesses are limited to 10 nm. The FMR results display multipeaked spectra, where we have identified three Fe resonance lines in the RM sample and an extra two in the ES sample. Angular FMR studies show a strong uniaxial anisotropy induced in the Fe layer via the strong exchange coupling with the FePt film. An additional uniaxial component is also observed with an easy axis inclined by about 50 ^deg from the film normal. Supplementary magnetic measurements aid with the magnetic characterization. We also discuss the elements for the theory of FMR in these exchanged coupled systems.