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