[Show abstract][Hide abstract] ABSTRACT: Magnetoresonance (in the frequency range 22–80 GHz) and magnetostatic studies of the La1−xSrxMnO3 compound with strontium impurity concentrations x = 0.15; 0.225; 0.3; 0.45; 0.6, performed at room and liquid helium temperatures. A splitting of the electron magnetic resonance curve is detected for x = 0.3, which serves as evidence of mixed magnetic phases. The samples' concentration dependences of saturation
magnetization are determined based on the obtained experimental data.
Low Temperature Physics 04/2015; 41(4):273. DOI:10.1063/1.4918758 · 0.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The experimental study of Double Negative (DNG) state of electromagnetic wave propagating in lanthanum manganite-perovskites doped with strontium La1-xSrxMnO3 is provided firstly below individual Curie temperatures (in ferromagnetic metal state (FM) for La1-xSrxMnO3). Various dopant concentrations are considered for ceramic specimens: x = 0.15; 0.225; 0.3; 0.45; 0.6. It is shown that dependence of the DNG-peak intensity on dopant concentration is sharply non-monotone with maximum at the dopant concentrations x = 0.225 - 0.3. This behaviour follows the change of Curie temperature with increase of dopant concentration in such substances. The obtained dependence of DNG peak intensity supports the opinion concerning the role of disorder in highly doped manganite-perovskite magnetic ceramics under study.
[Show abstract][Hide abstract] ABSTRACT: Spin wave spectra of 40-nm thick perpendicularly magnetized circular Permalloy dots of 250 nm radius were measured using ferromagnetic resonance technique in 70-80 GHz range at 4.2 K and in 10 GHz at room temperature. The five sharp resonance peaks were observed for both frequency ranges. The resonance fields can be well described by a magneto-exchange dispersion relation, implying that the observed resonances correspond to circular “drumhead” modes with Bessel-function profiles. The relative distances between neighbor peaks for different frequency ranges were almost the same, while the absolute interpeak distances in millimeter range were ∼30% bigger than at 10 GHz, as predicted by the theory.
[Show abstract][Hide abstract] ABSTRACT: This paper reviews research into a little-studied phenomenon in which strong stray fields arise in ferromagnets with giant magnetic anisotropy. Conditions for this to occur and for the fields to be stable are discussed. A classification of strong fields is presented. For different field types, limiting field strength values on approaching singular points are determined. Applications of the stray fields in various technical devices are considered.
[Show abstract][Hide abstract] ABSTRACT: The Tamm states  in quantum mechanics of bounded periodical crystals are well known special surface state of electrons concentrated in the vicinity of the crystal boundary. There are two physical reasons of electron localization near the surface: the electron motion outside, in the vacuum, is restricted by existing potential barrier connected with work function of a metal, while inside crystal the electronic motion is restricted if its energy belongs to an electron forbidden zone in periodic lattice. Tamm level shows itself as a very narrow level in the forbidden zone of electron spectra.
Physics and Engineering of Microwaves, Millimeter and Submillimeter Waves (MSMW), 2013 International Kharkov Symposium on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: The term “Tamm states” arose from the famous work of Igor Tamm, who predicted the appearance of surface states at the boundary of periodic crystal lattice. Later the term was widely used for theoretical description of electromagnetic wave propagation in bounded one-dimensional photonic crystals (PCs). As it is known, PCs are also periodic structures consisting (for example) of layers with different permittivity. In the case when the periodic structure (the PC) is bounded by the metal-like medium (wire-medium or some other media in which electromagnetic waves cannot propagate due to the strong attenuation) electromagnetic surface Tamm states appear at the interface.
Physics and Engineering of Microwaves, Millimeter and Submillimeter Waves (MSMW), 2013 International Kharkov Symposium on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Review discusses some special questions of physics of composite media (metamaterials), which are formed by elements made from natural materials of two kinds. The first ones are “carriers of permittivity” and are presented by plasma-like media and semiconductors. The second ones are “carriers of permeability”—they are presented by ferromagnets. Among such ferromagnets are ferrodielectrics (ferrites) and manganite-perovskite compounds. In the first chapter of the review some principal aspects of the electrodynamics of periodical structures—magnetophotonic crystals are considered. The questions of zone structure and possible violations of periodicity (Tamm states, defect mode) as well as the influence of external magnetic field on the spectral characteristics of magnetophotonic crystals are considered. The second chapter of the review is devoted to the electrodynamics of left-handed media (left-handed metamaterials). Different versions of composite left-handed media are considered. Particular attention is paid to features of electrodynamics of artificially synthesized left-handed media, the doped lanthanum manganites-perovskites, which in a certain concentrations of doping element and temperature range can serve as an example of natural left-handed media. The Appendix describes the details of experimental techniques radiophysical research. Note that the research and design of the metamaterials listed above in a range of low temperatures are particularly important. This is due to the fact that at low temperatures a main disadvantage of artificial materials mentioned above (quite large losses) becomes less noticeable. At the same time the main their advantage (namely the possibility to control their frequency dispersion) remains. Thus it seems that the most prospective areas of application and further study of the magnetic metamaterials lie at low temperatures.
Low Temperature Physics 07/2012; 38(7). DOI:10.1063/1.4733684 · 0.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The paper is devoted to experimental study of Faraday Effect enhancement. The experimental structure consists of photonic crystal, loaded with ferrite, which in turn is covered by thin metal layer or wire medium. An analysis of the transmission/reflection spectra for both unloaded and loaded photonic crystals shows that the surface oscillation mode (the surface state) is formed in the crystal band gap. A good agreement exists between experimental data and numerical calculations.
Solid State Phenomena 06/2012; 190:365-368. DOI:10.4028/www.scientific.net/SSP.190.365
[Show abstract][Hide abstract] ABSTRACT: The left-handed features of Sr doped manganite lanthanum ceramics La0.775Sr0.225MnO3 in the vicinity of its Curie temperature are studied. The left-handed features are responsible for appearance of the additional transparency peak in the forbidden band of the photonic crystal bounded with the above manganite. The magnitude of the critical exponent β (β ∼ 0.50) determined in the work agrees with results reported in the literature and allows supposing that long-range interactions play an important role in the phase transition from conductive ferromagnetic to nonconductive dielectric paramagnetic state of the manganite in its Curie point.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Tunneling of microwave radiation through the surface Tamm state that is generated at the interface between two different periodic
structures (photonic crystals) has been studied theoretically and experimentally. The possibility of controlling the transmission
frequency of this system with the use of an external magnetic field has been predicted theoretically and confirmed experimentally.
Physics of the Solid State 07/2010; 52(7):1427-1431. DOI:10.1134/S1063783410070176 · 0.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper the realization of concept of "continuous" left-handed medium, after entering which the electromagnetic wave changes the sign of its phase velocity, is studied for one-dimensional composite with the help of computer simulation. For the ID composite, formed by elementary cells of ferrite layer and wire medium the concept of "continuous" left-handed medium holds for λ > 6d.
[Show abstract][Hide abstract] ABSTRACT: We accumulated here the technique for measuring the electrodynamic constitutive parameters (the effective permittivity and permeability) for some 1D (one dimensional) metamaterials formed by the natural materials. The question of transfer form the radiofrequency band up to optical frequencies is under discussion.
[Show abstract][Hide abstract] ABSTRACT: Left-handed behavior of strontium-doped lanthanum manganite was revealed in the millimeter waveband. The bulk specimen of La <sub>1-x</sub> Sr <sub>x</sub> MnO <sub>3</sub> , 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.
[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of Physics D Applied Physics 02/2009; 42(5):055003. DOI:10.1088/0022-3727/42/5/055003 · 2.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Stray fields produced by magnets in the form of a cylinder in which the vector of magnetization at each point is directed along the cylinder radius have been calculated. It was assumed that this distribution of magnetization was achieved due to the presence of a radial crystalline texture and the related magnetic anisotropy with a large field of the uniaxial anisotropy H K . It has been shown that the greatest stray fields are reached on the surface of the magnet at points that are located near its axis, and the limiting value of the point field is equal to 4pi M S ln( a/r). It has been established that in magnets with a radial magnetization the region of localization of strong fields H > 4pi M S substantially exceeds that characteristic of the systems of magnets with a uniform magnetization.
The Physics of Metals and Metallography 02/2009; 107:133-140. DOI:10.1134/S0031918X09020045 · 0.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Three systems of permanent magnets, which produce strong magnetic stray fields (SFs) with H>Br=4piMr were studied in this work. Remarkable feature of the developed systems is localization of the strong fields in large region with linear dimension Deltar comparable to characteristic magnet dimension a. The first system composed of uniformly magnetized magnets generates sufficiently homogeneous strong SFs, which amounts up to 1.5 of magnets induction Br. The second system with nonuniform magnetization is represented by cylindrical and hemispheric magnets their magnetization vector directed at every point along the radius. Such distribution of magnetization is assumed to be the consequence of magnet radial crystal texture resulting in a high uniaxial anisotropy field HK. It is shown that maximal SFs can exist on the flat surface of cylindrical magnet at the distance r from its axis and their limiting value equals to 4piMr ln(2a/r). Here, the localization region of the fields is comparable to diameter of cylindrical magnet Deltar≈2R. As for the hemisphere its SFs are less than corresponding SFs for the cylinder. The third so-called quasi-nonuniform system consists of uniformly magnetized cylindrical sectors their magnetization vector is directed along the sector bisectrix. The strong SFs and their localization region are calculated in details for this case. The passage to radial magnetized cylinder is considered.
Journal of Magnetism and Magnetic Materials 04/2008; 320(8):1490-1498. DOI:10.1016/j.jmmm.2007.12.017 · 1.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The nonpropagating surface modes (surface states) of electromagnetic waves on the interface of 1-D ferrite based magnetophotonic crystal (MPC) adjacent to various opaque media have been studied theoretically and experimentally in the millimetre waveband. These states are direct analogue of non-travelling Tamm surface states in condensed matter physics and correspond to localization of electromagnetic field near the interface. Opaque media are represented with the system of wires (ldquowire mediumrdquo) or another photonic and magnetophotonic crystal in stop-band. The Tamm peak was identified experimentally and its position in the frequency gap of MPC was calculated.
[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of Physics D Applied Physics 01/2007; 40(2):295. DOI:10.1088/0022-3727/40/2/001 · 2.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Various systems of permanent magnets with a large magnetic anisotropy, in which strong stray magnetic fields are generated,
have been calculated. A classification of the magnet systems and corresponding strong fields into linear and point systems
is suggested. It is shown that the greatest linear field can be obtained in a system of the Halbach-cylinder type, in which
this field tends to H
sln(a/x) with increasing number of uniformly magnetized sectors. The limiting value of the point field is obtained in systems of
a large number of conical magnets each separated into many sectors. Such a field approaches H
sln(a/x) in magnitude.
The Physics of Metals and Metallography 10/2006; 102(5):494-505. DOI:10.1134/S0031918X06110068 · 0.76 Impact Factor