On the interpretation of the angular dependence of the FMR spectrum in   heterogeneous ferromagnetic thin films
  We demonstrate that a multi-peak FMR spectrum, with lines corresponding to resonance in different ferromagnetic regions of a heterogeneous thin-film sample, can collapse to a single-peak spectrum if there exists a particular field configuration, or the configuration of the external magnetic field with respect to the film surface, in which $dH_{\text{res}}/dM_{\text{eff}}=0$ within the region magnetically dominating in the sample. 
Maciej Kasperski and Henryk Puszkarski
cond-mat.mtrl-sci cond-mat.other