Thesis describes a novel Broadband Ferromagnetic Resonance (FMR) Spectrometer designed to characterize new iron garnet materials. The spectrometer uses two probeheads: one is the X-band microwave reflection cavity for express room temperature measurements and the in-cryostat microstrip line probe to perform FMR experiments in the frequency range 50 MHz to 40 GHz. Very uniform and stable magnetic field up to 2.4 T, temperature 4 K to 420 K, and continuous frequency scan performed by HP8722D vector network analyzer provide various modes of operation. Both probeheads are equipped with two-circle goniometers to ensure accurate measurements of magnetic anisotropy.

   The spectrometer was used to make express-analysis of quality thus to optimize processing parameters of epitaxial iron garnet films by pulsed laser deposition  (PLD). Comprehensive study of uniaxial and cubic magnetocrystalline anisotropy has been performed for Y₃Fe₅O₁₂ and Bi₃Fe₅O₁₂ films grown on different substrates by PLD and reactive ion beam sputtering. Broad band FMR-spectroscopy revealed difference in spectra of domain wall resonances: instead of “soft” spin modes in films grown by liquid phase epitaxy (LPE), PLD-made films show “diffuse” transformation of domains near the saturation field. This effect indicates non-uniformity of saturation magnetization and field of uniaxial anisotropy in PLD-iron garnets. Magnetooptical study of Ce:Y₃Fe₅O₁₂ single crystal complements results of FMR-spectroscopy.