Rotatable anisotropy of Ni81Fe19/Ir20Mn80 films: A study using broadband ferromagnetic resonance

We investigate the broadband ferromagnetic resonance dispersion relation of NiFe/IrMn multilayers using the vector network analyzer ferromagnetic resonance (VNA-FMR) method. Multilayered films with structure [NiFe(20 nm)/IrMn (tIrMn)/Ta(3 nm)]×10 (with tIrMn=4 and 15 nm) were produced onto Si(100) substrates using magnetron sputtering. The dispersion relations of the samples were extracted from the resonance spectra in the range of 0.1-7 GHz under magnetic fields of up to±300 Oe. Static magnetization curves were also obtained in the same field range. The experimental data were compared with numerical calculations performed using the granular exchange-bias model which takes into account both, the unidirectional and rotatable anisotropy present in the samples. A good agreement between numerical and experimental results was achieved without the need of any frequency or field-dependent parameter.