  In this work, magnetization dynamics is studied at low temperatures in a
hybrid system that consists of thin epitaxial magnetic film coupled with
superconducting planar microwave waveguide. The resonance spectrum was observed
in a wide magnetic field range, including low fields below the saturation
magnetization and both polarities. Analysis of the spectrum via a developed
fitting routine allowed to derive all magnetic parameters of the film at
cryogenic temperatures, to detect waveguide-induced uniaxial magnetic
anisotropies of the first and the second order, and to uncover a minor
misalignment of magnetic field. A substantial influence of the superconducting
critical state on resonance spectrum is observed and discussed.
