In situdetection of two ferromagnetic resonance modes in coupled Ni/Cu/Co/Cu(001) trilayer structures

Abstract

Ultrathin Ni and Co films, separated by Cu spacer layers with thicknesses in the range 4--15 monolayers, are prepared and measured in situ via ferromagnetic resonance (FMR) between 50 and 400 K. Due to the interlayer exchange coupling two resonance modes are observed, corresponding to in- and out-of-phase precession of the rf magnetizations in the two magnetic layers, i.e., the acoustic and optic mode. The fields for resonance ${H}_{\mathrm{res}}$ and the linewidths $\ensuremath{\Delta}{H}_{\mathrm{pp}}$ of the exchange coupled FMR modes are measured as a function of temperature. Since all the measurements are performed in situ, we can compare the signal of the first (bottom) magnetic layer before and after the evaporation of the second (topmost) one. For the coupled films we observe an increase of $\ensuremath{\Delta}{H}_{\mathrm{pp}}$ compared to the uncoupled case. From the shift of ${H}_{\mathrm{res}}$ after the deposition of the second layer the sign and relative strength of the coupling is derived.