S. I. Tarapov

Magnetically controllable 1D magnetophotonic crystal in millimetre wavelength band

We analyse the results of experimental and theoretical studies of a 1D magnetophotonic crystal based on the ferrite magnetic periodic multilayered structure. The adequacy of the proposed phenomenological model for description of this crystal in the millimetre waveband is tested experimentally. The possibility to control the spectra of such a structure by variation of the external magnetic field is demonstrated. It is shown that detuning of frequency stop-bands in the spectrum is determined first of all by dispersive properties of the ferrite. The promising applications of such structures as tunable extra high frequency devices are discussed.

Left-handed behavior of strontium-doped lanthanum manganite in the millimeter waveband

Left-handed behavior of strontium-doped lanthanum manganite was revealed in the millimeter waveband. The bulk specimen of La 1 − x Sr x MnO 3 , was used as a boundary medium for one-dimensional photonic crystal. In the absence of magnetic field known Tamm peak appears in the forbidden zone of photonic crystal indicating that manganite is a single negative medium (negative permittivity). In the presence of external magnetic field somewhat above frequency of ferromagnetic resonance the additional (field sensitive) transparency peak appears in photonic crystal forbidden zone, indicating that manganite becomes double negative medium (negative permittivity and permeability). Model theoretical calculations corroborate the experimental findings.

Tamm states in magnetophotonic crystals and permittivity of the wire medium

The system consisting of a magnetophotonic crystal (MPC) and a medium with negative permittivity was studied both experimentally and theoretically. The medium was prepared as a set of conductive wires?wire medium (WM). The MPC elementary cell comprises three layers (air, ferrite and quartz). The Tamm state (TS) position in a stop band was calculated depending on the thickness of the air layer in an MPC elementary cell and on the value of the WM negative permittivity. Using the experimental value of the TS frequency the inverse problem was solved and the effective permittivity of the WM bounding the MPC was obtained.

Negative permittivity and left-handed behavior of doped manganites in millimeter waveband

The “effective plasma frequency” of strontium-doped lanthanum manganite was determined basing on its double negative properties. The zone of high transmission (double negative zone) for spatially partitioned layered manganite specimen, immersed into dielectric matrix, was studied experimentally in millimeter waveband. It turns out that frequency dependence of manganite permittivity is well described by Drude formula, which includes only one parameter—the “effective plasma frequency.” Additionally, the negativity of the refraction index has been directly proved in experiments studying electromagnetic waves refraction in manganite prism.

Microwave experiments in He II. New features of undamped superfluid flows

The stability and oscillatory properties of superfluid ring flow arising around the cylindrical surface of a disk-shaped dielectric resonator immersed in liquid helium are studied experimentally. The velocity of superfluid flow is controlled with special heat guns, placed in He II and generating counterflows of the normal and superfluid components, directed along the tangent to the cylindrical surface of the resonator. In the experiment the amplitude of the microwave signal passing through the resonator is measured and the effect of the phase and dynamic states of the liquid on the signal amplitude is studied. It is found that periodic oscillations of the signal are observed in the He II state, and each period starts with a sharp spike of the amplitude. It is proposed that this behavior signifies instability of superfluid ring flow due to a change in the number of circulation quanta of the superfluid velocity over a very short time. Another effect is due to the appearance of new periodically repeating res...

Resonance excitation of single rotons in He II by an electromagnetic wave. Spectral line shape

The amplitude-frequency characteristic of the spectral line of electromagnetic absorption in liquid helium is measured in the frequency range 40–200GHz at temperatures in the interval 1.4–2.75K. It is found that in the roton frequency region a narrow resonance absorption line on a broad pedestal is observed. The results are compared with data on the roton spectrum found in neutron scattering experiments in liquid helium. The narrow line is due to the creation of a single roton. It is shown that the momentum conservation law is satisfied on account of the transfer of momentum to the superfluid component. The analogy of this effect with the Mossbauer effect is pointed out.

Interaction of microwaves with superfluid flow in HeII

The absorption of 40–200GHz electromagnetic waves in liquid helium at temperatures 1.4–2.8K is investigated experimentally. The spectrum of oscillations of the “whispering gallery” modes of a dielectric disk-shaped resonator immersed in liquid helium is recorded. Superfluid flows in HeII is produced artificially using two “heat guns.” A narrow microwave absorption line has been detected at a frequency corresponding to the excitation energy of a single roton. It has been determined that the character of the resonance line changes radically as the velocity vs of the superfluid flow increases: microwave absorption was replaced by induced microwave emission, which was seen as a sharp intensification of the high frequency signal. The effect can be explained qualitatively on the basis of a two-level model of HeII. An abrupt change in the velocity of the superfluid flow is observed with continual increase of the power delivered to the heat gun. This could attest to quantization of vs. It is shown that the superf...

Microwave-frequency spin-dependent tunneling in nanocomposites

The transmission coefficient of films of Co51.5Al19.5O29, Co50.2Ti9.1O40.7, Co52.3Si12.2O35.5, and (Co0.4Fe0.6)48(MgF)52 ferromagnetic metal-insulator magnetic nanocomposites exhibiting tunneling magnetoresistance and the magnetorefractive effect for electromagnetic waves was studied in the frequency range 30–50 GHz. The transmission coefficient of the first two compositions varies strongly under an applied magnetic field, and its variation exhibits a linear correlation with the field dependence of magnetoresistance. For the other two compositions, the transmission coefficient does not depend on magnetic field. The data obtained are interpreted in terms of the concept of microwave spin-dependent tunneling.

Resonant features of planar Faraday metamaterial with high structural symmetry - Study of properties of a 4-fold array of planar chiral rosettes placed on a ferrite substrate

The transmission of electromagnetic wave through a planar chiral structure, loaded with the gyrotropic medium being under an action of the longitudinal magnetic field, is studied. The frequency dependence of the metamaterial resonance and the angle of rotation of the polarization plane are obtained. We demonstrate both theoretically and experimentally a resonant enhancement of the Faraday rotation. The ranges of frequency and magnetic field strength are defined, where the angle of polarization plane rotation for the metamaterial is substantially higher than that one for a single ferrite slab.

Electron Spin Resonance Properties of Magnetic Granular GMI—Nanostructures in Millimeter Waveband

The millimeter waveband giant magnetoimpedance (GMI) and magnetoresonance (FMR) properties of thin-layered magnetic nanostructures are analyzed experimentally for wide temperature range. The correlation between FMR and GMI features are under discussion. The manifestation of the anisotropy established by the millimeter waveband FMR experiments and possible reasons of anisotropy appearance are given.