Broadband Ferromagnetic Resonance Spectrometer Instrument and Applications

University dissertation from Kista : Mikroelektronik och informationsteknik

Abstract: This thesis compiles results of research in two mutuallydependent parts: 1) development of ferromagnetic resonance(FMR) spectrometer to study microwave properties offerromagnetic materials, and 2) characterization of new irongarnets: pulsed laser deposited Y3Fe5O12and Bi3Fe5O12films and Ce:Y3Fe5O12single crystal.First part describes a novelBroadbandFMRSpectrometerdesigned to characterize thin ferromagneticfilms. The spectrometer uses two probeheads: one is the X-bandmicrowave reflection cavity for room temperature measurementsand the in-cryostat microstrip line probe to perform FMRexperiments in the frequency range from 50 MHz to 40 GHz. Veryuniform and stable magnetic field up to 2.4 T, temperatures 4 Kto 420 K, and continuous frequency scan performed byHP8722Dvector network analyzer provide various modes ofoperation. Both probeheads are equipped with two-circlegoniometers to ensure accurate study of magneticanisotropy.The spectrometer was used to make express-analysis ofquality thus to optimize processing parameters of epitaxialiron garnet films grown by pulsed laser deposition (PLD).Comprehensive study of uniaxial and cubic magnetocrystallineanisotropy has been performed for Ce:Y3Fe5O12bulk crystal as well as for Y3Fe5O12and Bi3Fe5O12films grown on different substrates by PLD andreactive ion beam sputtering techniques. BroadbandFMR-spectroscopy revealed difference in spectra of domain wallresonances: instead of?soft?spin modes in filmsgrown by liquid phase epitaxy, PLD-made films show?diffuse?transformation of domains near thesaturation field. This effect indicates non-uniformity ofsaturation magnetization and field of uniaxial anisotropy inPLD-iron garnets. Spin wave resonances in comparison withuniform FMR have been studied to evaluate?localquality?of ferromagnetic films. The resonance field andFMR linewidth behavior were studied at various crystallographicdirections determined by X-ray diffraction.FMR was used to choose PLD-made YIG films with low losses atmicrowave frequencies and to build magnetostatic surface wavesmicrowave bandpass filter. The filter was designed as a planarfilm structure with a microstrip line for transducers. It is afirst demonstration of feasibility to introduce PLD processingtechnique to magnetostatic wave technology.Magneto-optical study of Ce:Y3Fe5O12single crystal complements results ofFMR-spectroscopy of new garnets.Keywords:ferrites, thin films, ferromagnetic resonance,microwaves, FMR spectrometer, magnetic anisotropy,magnetostatic waves.