Unraveling intricate properties of exchange-coupled bilayers by means of broadband ferromagnetic resonance and spin pumping experiments

Abstract

Ferromagnetic resonance (FMR) measurements using a broadband microstrip excitation technique were performed at room temperature for an antiferromagnetic/ferromagnetic (AF/FM) bilayer of ${\mathrm{Ir}}_{20}{\mathrm{Mn}}_{80}(35.0\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/{\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}(7.5\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$. The angular dependence of the resonance field was measured for several excitation frequencies ranging from $1.5$ to $10.0$ GHz. From the numerical fitting of the experimental data, it was observed that the exchange bias field $({H}_{E})$ and the rotatable anisotropy field $({H}_{\mathrm{RA}})$ originating from the exchange interaction at the AF/FM interface are frequency dependent. The results were explained considering the coexistence of ferromagnetic and antiferromagnetic coupling at the AF/FM interface. We also investigated the spin pumping voltage generated in the structure of ${\mathrm{Ir}}_{20}{\mathrm{Mn}}_{80}(35.0\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/{\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}(7.5\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$/Pt(4 nm) and showed that from the voltage peaks occurring at the ferromagnetic resonance condition it is possible to reproduce the FMR dispersion relation.