Determination of Exchange and Rotatable Anisotropies in Co₂FeSi/IrMn Exchange Coupled Structures using Broadband Ferromagnetic Resonance

We determined exchange $H_{ex}$ and rotatable $H_{rot}$ anisotropy fields of multilayers that comprise 10 nm Co₂FeSi (CFS) layers exchange coupled to 20 nm IrMn layers by using ferromagnetic resonance with a vector network analyzer (VNA-FMR). The multilayer structures consist of IrMn/bottom (b)-CFS/IrMn/middle (m)-CFS/IrMn/top (t)-CFS/IrMn layers so that each CFS layer is surrounded by a pair of IrMn layers. In the structures, the exchange bias field propagates in such a way that $H_{ex}^{t}$ > $H_{ex}^{m}$ > $H_{ex}^{b}$ for the top, middle, and bottom layer, respectively. FMR response measured along the exchange bias (EB) axis consist of only two absorptions related to the (b+m)- and (t)-CFS layers, respectively. Exchange and rotatable anisotropy determined independently from angular and dispersion measurements of the resonance fields are nearly the same. Rotatable anisotropy field scales with the exchange bias field in these complex structures.