Sub-Terahertz Magnetic and Dielectric Excitations in Hexagonal Ferrites

Abstract

Magnetic and dielectric resonances in the sub-terahertz (sub-THz) frequency range are observed in pure and Al-substituted hexagonal barium ferrite. A resonator based on magnetic excitations has been fabricated and its performance characteristics have been studied. The possible use of the resonator at sub-THz frequencies has been demonstrated. The resonator exhibited a loaded Q-factor of 150-330 in the frequency range 97-108 GHz. Dielectric resonances in a single-crystal barium hexaferrite are observed in the frequency range 75-110 GHz. The modes excited by circularly polarized electromagnetic waves show nonreciprocal propagation characteristics. The dielectric resonances may occur at a much higher frequency than ferromagnetic resonance. It is shown that degeneracy in the dielectric modes is lifted with an applied magnetic field and that the modes can be tuned by 10 GHz or more with . Data on frequencies of the modes versus shows hysteresis. Theoretical predictions on -tuning characteristics of the principal dielectric 11 mode are in agreement with the data. The dielectric modes are of importance for the realization of low-loss devices, including resonators, isolators and phase shifters.

A Magnetic Field Tunable Yttrium Iron Garnet Millimeter-Wave Dielectric Phase Shifter: Theory and Experiment

“…In YIG samples zero-field splitting of counter rotating mode frequencies is present, contrary to observations for dielectric resonance in barium hexaferrites (BaM) disks [7]. It could be a consequence of differences in the domain structures [12,27,28]; domains in BaM are much smaller and after spatial averaging its zero-field highfrequency properties more resemble a pure dielectric.…”

“…For the larger disk (Sample A) lower-order dielectric resonance E 11δ [7] lies in the U-band (40-60 GHz), whereas for the smaller disk (Sample B) has the resonance in the W-band (75-110 GHz). YIG was chosen due to its excellent dielectric properties (dielectric losses tangent ≈ 2 · 10 −4 [8]) and low saturation magnetization (i.e., low tuning magnetic field).…”

High frequency magneto-dielectric effects in self-assembled ferrite-ferroelectric core-shell nanoparticles

“…A similar device application, H-tunable dielectric resonators, phase shifters, or isolators could be envisioned for dielectric resonance in the core-shell composites. 50 Such device use also would require efforts directed at reduction of the line-width for the resonance in Fig. 5.…”

Structural and millimeter-wave characterization of flux grown Al substituted barium hexaferrite single crystals

“…Hexagonal ferrites with large magnetocrystalline anisotropy are promising for mm-wave applications as well as for use in sub-terahertz range. In particular, tunable resonators [17][18][19][20][21], isolators [22] and radio-absorbing coatings [13] were developed with the use of films or bulk hexaferrite materials. In this context the elaboration of a robust technology for production of hexaferrite single crystals became important in recent years [23][24][25].…”

“…The magnetic and millimeter-wave properties of the compositional series of BaFe 12 À x Al x O 19 grown by the floating zone melting method were already presented [17][18][19]. Recently, we were able to grow single crystals of BaFe 12 À x Al x O 19 with x in the range of 0 to 1.1 by the flux technique [16].…”