Quality factor of magnetostatic oscillations in (111)-YIG films

The paper presents results of theoretical study of the intrinsic quality factor for various types of magnetostatic oscillations in ferrite film resonators. The limits of variation of the Q-factor are investigated in the frequency range allowing for existence of the respective oscillation modes depending on the magnetization field

Tunable reflective structures based on weak ferromagnetics and their application as tunable sub-terahertz resonators

Electromagnetic eigenwaves in a weak ferromagnetic with anisotropy of the “easy plane” under magnetization in this plane are investigated. It is shown that at frequencies of anti-resonances the weak ferromagnetic can be considered as environment with characteristic impedance close to zero. The polarization of eigenwaves in such environment is analyzed on the example of high-temperature weak ferromagnetics—hematite and iron borate. It is proposed to consider the weak ferromagnet–metal structure as an element of the metasurface with a controlled phase shift of the reflected wave. A tunable Fabry–Perot resonator with a weak ferromagnet–metal structure (ferromagnet is of sub-wave thickness) is considered and the corresponding frequency-field dependencies in the sub-terahertz range are studied. It is shown that such resonator combines rather high Q-factor with a possibility of magnetic tuning of its resonance frequency. The maximum local slope of the field dependence of the resonator frequency reaches 0.3 MHz/Oe using a hematite layer and 0.6 MHz/Oe using an iron borate layer of 10 mm thickness. The resonator unloaded quality factor for the main mode varies within 300–1400 and 250–1000, respectively

Frequency splitting effect of degenerate modes in ferrite resonators

The splitting of magneto-dielectric modes frequency in disk ferrite resonators in a magnetic field is considered. A simplified formula is obtained for estimation of the splitting magnitude. Theoretical and experimental results of the frequency splitting effect in magneto-dielectric modes in the millimeter wave range are compared. The use of the splitting of the magneto-dielectric modes frequencies as an alternative to ferromagnetic resonance in devices with magnetic frequency tuning is suggested, with values of the magnetization fields being an order of magnitude lower than for ferromagnetic resonance. The features of the splitting modes effect in different ferrite classes are investigated and it is shown that it occurs in both microwave and optical ranges. The estimated magnitude of the mode frequency splitting in the iron-yttrium garnet (YIG) transparency window can reach 9 GHz, which is comparable to the 5 GHz splitting in the millimeter range. The frequency ranges where frequency splitting effect is of practical interest are discussed. In particular, the effect in barium hexaferrite can be used both in post-resonance and pre-resonance regions, which is almost impossible for ferrogarnates and ferrospinels

Dual electric and magnetic frequency tuning of coupled oscillations in a composite magnetodielectric resonator

The possibility of dual magnetic and electric tuning of resonance frequencies of the electrodynamic structure consisting of dielectric resonator and the epitaxial film of Yittrium-Iron Garnet (YIG)- lead zirconate titanate (LZT) heterostructure has been shown. The coupled electromagnetic-and- spin oscillations of dielectric resonator and epitaxial YIG film were theoretically and experimentally investigated. The experiments revealed the possibility of implementing the electric frequency tuning of coupled oscillations of a composite magnetodielectric resonator. This possibility is determined by induced elastic stresses in the epitaxial YIG film. A theoretical model is proposed for calculating the frequency shift of coupled oscillations caused by the electric field applied to the piezodielectric layer. It is shown that the basic Q-factor of composite resonator and the range of electric frequency tuning of hybrid oscillations increase with the reduction of the magnetic bias field

Electrodynamic characteristics of T-mode coaxial waveguides with elliptical cross-section

The paper presents a rigorous solution of the electrodynamic problem for T-type waves in a coaxial waveguide of elliptical cross-section. The solution was obtained using the original modified elliptical coordinate system. The advantages of this approach are convenient expressions for the electrodynamic characteristics of the transmission line and a simple transition to a particular case of a circular waveguide. The authors have obtained explicit expressions for the impedance, transmitted power and propagation losses of the coaxial elliptical waveguide with T-type waves, and have analyzed their dependences on the size and shape of the cross-section of the transmission line. The graphs of the dependences of these characteristics on the normalized parameters that define the shape and size of the waveguide allow choosing the geometric dimensions of the transmission line based on the requirements of a given characteristic impedance, limiting transmitted power or losses. It is shown that at large eccentricities, the energy in waveguides with similar sizes of internal and external conductors and low wave resistance is concentrated near the foci, which allows using such waveguides as the basis for developing effective probes for radio-spectroscopic studies

Splitting axially heterogeneous modes in microwave gyromagnetic and gyroelectric resonators

Theory of calculating eigenmodes spectrum for gyrotropic resonators when using scalar potentials formalism is developed. Equations for calculating splitting of resonant frequencies of gyromagnetic and gyroelectric cylinder resonators in magnetic field are derived. Theoretical results are compared to the experimentally obtained figures for microwave gyromagnetic resonators made of barium hexaferrite. Example of a resonator made of indium antimonide demonstrates the possibility of using magnetized semiconductor resonators cooled to liquid nitrogen temperature to achieve the same characteristics offered by resonators made of magnetically firm hexaferrites when designing unidirectional microwave devices

Fast long-wavelength exchange spin waves in partially compensated Ga:YIG

Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing attention from the perspective of novel magnon-based data processing applications. For short wavelengths needed in small-scale devices, the group velocity is directly proportional to the spin-wave exchange stiffness constant λex⁠. Using wave vector resolved Brillouin light scattering spectroscopy, we directly measure λex in Ga-substituted YIG thin films and show that it is about three times larger than for pure YIG. Consequently, the spin-wave group velocity overcomes the one in pure YIG for wavenumbers k > 4 rad/μm, and the ratio between the velocities reaches a constant value of around 3.4 for all k > 20 rad/μm. As revealed by vibrating-sample magnetometry and ferromagnetic resonance spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert damping (⁠α<10−3⁠), a decreased saturation magnetization μ0MS≈20 mT, and a pronounced out-of-plane uniaxial anisotropy of about μ0Hu1≈95 mT, which leads to an out-of-plane easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport for all wavelengths in nano-scale systems independently of dipolar effects