Dependence of the ferromagnetic-resonance parameters of polycrystalline ferrites on uniaxial elastic stress

Methods developed for taking into account the effect of magnetic crystallographic anisotropy on ferromagnetic resonance in polycrystalline ferrites are used to calculate the dependence of the line width of resonant ferromagnetic absorption and the magnitude of the resonant field of polycrystalline ferrites on uniaxial elastic stress.Translated from Izvestiya Vysshikh Uchetanykh Zavedenii Fizika, No. 10, pp. 49–55, October, 1970.     

Ferromagnetic resonance in polycrystalline ferrites with high magnetic anisotropy

The ferromagnetic resonance absorption line is computed in polycrystalline ferrites in the independent grain approximation taking account of the magnetic crystallographic and magnetostriction anisotropies. The results obtained show that the influence of elastic stresses on the shape of the absorption line is analogous to the effect of the magnetic crystallographic anisotropy.Translated from Izvestiya VUZ. Fizika, No. 1, pp. 9–16, January, 1972.     

Energy dissipation in high-frequency remagnetization of ferrites

The frequency dependence of magnetic loss in ferrites at various exciting field amplitudes is studied. A model is constructed from which losses due to microeddy currents in hysteresis cyclical magnetization are estimated. Both the level and frequency dependence of losses observed in the vicinity of 100 kHz are explained within the framework of this model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 6–10, June, 1985.     

Ferromagnetic resonance line dispersion in polycrystalline ferrites

Results of a theoretical and experimental investigation of the influence of pores and nonmagnetic inclusions on the ferromagnetic resonance line dispersion in polycrystalline ferrites are elucidated in this paper. The absorption line dispersion is computed with the deflection of the local magnetization vector from the magnetizing field direction taken into account, where the dispersion is described by linear terms in the generation and annihilation operators in the Hamiltonian of the interacting spin wave system. The theory and experiment are compared in a broad range of variation of the porosity in different ferrites. The field of anisotropy of the ferrites investigated is calculated from the second moment of the absorption line.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 37–41, November. 1981.     

Equation of the ferromagnetic resonance line in polycrystalline ferrites

Ferromagnetic resonance in polycrystalline ferrites is considered in the framework of the independent-grain model. It is shown that the ferromagnetic resonance absorption line can be obtained analytically from its moments. When a limited number of moments of the line are known explicitly, the method of Pearson curves is used to obtain the equation of the line. The obtained expression is analyzed and the resonance field and absorption line width deduced from the equation are compared with results obtained earlier.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 19–23, March, 1981.     

Novel magneto-oscillatory behavior of confined electrons at a twin boundary in ZnSe and at an interface in GaAs/AlGaAs heterostructures

Electronic properties of confined electrons at naturally formed twin boundaries in ZeSe have been investigated by microwave absorption measurements. Cyclotron resonance signal of the confined electrons was observed. On the cyclotron resonance peak, novel oscillation of the absorption intensity was observed. Similar oscillatory behavior was also observed in GaAs/AlGaAs heterostructures near cyclotron resonance filed at which new Shubnikov–de Haas-like oscillation was observed by Zudov. The oscillatory structure has a period not in inverse magnetic field but magnetic field. The origin of the oscillation observed is caused by Rayleigh interference of two-dimensional electron gas.     

Effect of Zn substitution on the magnetic properties of Mg1−xZnxFe2O4 ferrites

Polycrystalline Mg_1−xZn_xFe₂O₄ (x=0.0–0.6) ferrites have been prepared using solid-state reaction technique. The X-ray diffraction analysis revealed that the samples crystallize in a single-phase cubic spinel structure. The lattice parameter increases linearly with increase in zinc content obeying Vegard's law. The continuous decrease in Curie temperature (T_c) with an increase in Zn content is attributed to the weakening of A–B exchange interaction. Saturation magnetization (M_s) and magnetic moment are observed to increase up to x=0.4, and thereafter decrease due to the spin canting in B-sites. The initial permeability is found to increase with the addition of Zn²⁺ ions but the resonance frequency shifts towards the lower frequency.     

Effect of pores and nonmagnetic inclusions on ferromagnetic resonance in polycrystalline ferrites

In this paper an account is given of the experimental results concerning the effect of pores and nonmagnetic inclusions on the ferromagnetic resonance line parameters in polycrystalline ferrites. Calculations of linewidth, resonance field, and first moment are compared with experiment in a wide range of porosity. The effect of porosity on the frequency dependence of the linewidth is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 112–115, February, 1982.     

Sensitivity of ferromagnetic-resonance parameters to uniaxial compression in polycrystalline ferrites

The width of the ferromagnetic-resonance absorption line and the resonance field in polycrystalline nickel aluminate ferrites were measured as functions of the uniaxial compression. Over a large part of the elastic-stress range studied the experimental results found agree with the results of a calculation carried out in the independent-grain approximation. Two magneto-striction constants are found from the experimental stress dependences of the line width and resonance field for these polycrystalline ferrites.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 2, pp. 36–40, February, 1971.     

A study of Fe grown on muscovite with Mössbauer spectroscopy

Mössbauer spectroscopy has been used to study Fe grown on muscovite by thermal evaporation in 10^–6 torr; there is evidence of hcp structure as far as thickness of 7,000 Å; no evidence was found for magnetic ordering. Quadrupole splitting of –0,42 mm/s is attributed to hcp Fe; the resonance lines are broader than that of bcc resonance lines. Results are presented on the isomer shift.     

Influence of CuO and sintering temperature on the microstructure and magnetic properties of Mg–Cu–Zn ferrites

The synthesis of a series of Mg–Cu–Zn ferrites with the substitution of Cu for Mg has been obtained by solid-state reaction method. Microstuctural and structural analyses were carried out using a scanning electron microscope and X-ray diffraction (XRD), respectively. The lattice parameter is found to increase with increasing copper content. A remarkable densification is observed with the addition of Cu ions in the ferrites. Microstructural analyses indicate that CuO influences the microstructure of the ferrites by the formation of liquid phase during sintering. The grain size significantly increases with increasing copper content. Exaggerated grain growth is observed for the samples of x=0.25–0.35. The initial magnetic permeability (μ′) increases sharply with increasing concentration of Cu ions. This increase in μ′ is explained with the grain growth mechanism and enhanced densification of the ferrites. The resonance frequency of all the samples shifts toward the lower frequency as the permeability increases with Cu content. Sintering temperature T_s also affects the densification, grain growth and initial magnetic permeability of the samples.     

High-frequency parameters of magnetic films showing magnetization dispersion

Magnetization dispersion leads to skewed resonance curves shifted towards higher magnetizing fields, together with considerable reduction in the resonant absorption, while the FMR line width is considerably increased. These effects increase considerably with frequency, in contrast to films showing magnetic-anisotropy dispersion, where they decrease. It is concluded that there may be anomalies in the frequency dependence of the resonance parameters for polycrystalline magnetic films.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 32–36, April, 1988.     

High power splitting of the cyclotron resonance induced photoconductivity in n-GaAs

Conclusion In summary our results show that photoconductivity and optical absorption under cyclotron resonance conditions in high purity n-GaAs are more complex than it has been assumed previously. As cyclotron resonance can only be measured with non zero free electron concentration, and because the 2p _– shallow donor level remains below the N=0 Landau level for all magnetic field strengths, a certain population of 2p _– states must be present and thus the interference between both absorption processes is unavoidable as long as 2p _–2p ₊ electric dipole transitions are activated by ionized impuritics. This interference gets most drastically manifest at high intensities causing an apparent splitting of the photoconductivity line. Even at lower intensities however when the dip in the photoconductivity line is not observable, all optical characteristics previously attributed to cyclotron resonance are affected by the shallow donor absorption. The energy separationE _2p+–E _2p– of shallow donors in a magnetic field is exactly equal to w _CR only for isolated impurities in the effective mass approximation. The same electric stray field of ionized impurities which cause the activation of 2p _–2p ₊ absorption may shift the donor energy levels due to stark effect. For magnetic field strengthsB<1 T a field dependent deviation ofE _{2 +}–E _{1p –} from the cyclotron resonance quantum energy was observed [15] amounting up to 8 pc. In this case we expect that the peak positions of photoconductivity and absorption do not spectrally coincide and do not occur at the resonance magnetic field strength of 01 Landau level transitions. Thus effective masses determined by standard cyclotron resonance methods at low magnetic fields may be incorrect by a few percent.     

Mössbauer study of the mixed ferrimagnetic-spin glass phase in SrFe12−x CrxO19 hexagonal ferrites

It is shown from zero magnetic field Mössbauer spectroscopy that the mixed ferrimagnetic-spin glass phase observed in SrFe_12–x Cr_xO₁₉ hexagonal ferrites is characterized by longitudinal spin components contributing to the ferrimagnetic long range magnetic ordering and transverse spin components contributing to the spin glass ordering. It is argued as well that different sublattices could behave in a different way owing to their different degree of magnetic frustration.     

Ferromagnetic Resonance Spectra in Single-Crystal Hexagonal Ferrites

Theoretical and experimental studies of ferromagnetic resonance in single-crystal hexagonal ferrites with different types of magnetocrystalline anisotropy (axis and plane of easy magnetization) are reported. The ferromagnetic resonance is examined in the 12–38 GHz frequency range in the state of homogeneous magnetization and in the presence of a strip domain structure inherent in materials with an axis of easy magnetization. This comprehensive ferromagnetic resonance investigation is shown to allow determination of not only anisotropy fields and g-factors but also saturation magnetization of a material from testing one sample alone. The anisotropy of g-factor of Zn₂Y is found experimentally.     

Theory of electronic light scattering in lateral superlattices with Rashba spin–orbit coupling under quantizing electric and magnetic fields

The influence of an in-plane electric and out-of-plane magnetic field on the electronic light scattering is calculated for a lateral semiconductor superlattice within Rashba spin–orbit interaction. Sharp resonances are predicted to appear when the Raman shift matches one frequency of the Wannier–Stark ladder. The spin–orbit interaction gives rise to a dispersion of the exact one-particle eigenstates and an associated finite width of the Raman line, which can be tuned by the electric and magnetic field. When the Bloch frequency is located in this Raman line, a Fano resonance is observed.     

Simultaneous determination of the temperature and density of rubidium vapor

We propose a new method for the simultaneous determination of the temperature and atom number density in rubidium vapor. The method is based on the comparison of theoretical simulations of the self-broadened absorption profiles of rubidium resonance lines with the measured profiles. Absorption measurements performed in rubidium vapor indicate that in the spectral region around resonance lines (760–835 nm), excellent agreement between theoretical and experimental absorption profiles can be achieved. In the temperature interval 500–700 K, the simultaneous determination of the atom number density and temperature of rubidium vapor is possible. We have applied the present method to nearly homogeneous and inhomogeneous rubidium vapors generated in a sapphire cell. PACS 31.15.Gy; 32.30.Jc; 32.70.-n     

The use of domain boundary resonance for study of the magnetization process in systems of lithium ferrites

The change in absorption spectra of lithium ferrite-aluminates produced by domain boundary resonance in an external magnetic field is studied. The character of the absorption spectrum change is compared with the real portion of the radio-frequency magnetic permeability as a function of the field. It is concluded that it is possible to study the process of magnetization by the domain boundary resonance method.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 52–56, July, 1973.     

Mixing effect in the NH3 absorption and MIR emission spectra pumped by a continuously tunable CO2 laser

By tuning a high pressure CO2 laser (HPL) around strong ammonia lines nearly coincident with CO2 lines an of-fresonant absorption is observed which can be confirmed by the superfluorescent MIR emission. This effect is related to a two frequency v₁, v₃ HPL emission in the regime of moderate pulling. Around a strong absorption line a mixed v₄=2v₁–v₃ frequency is produced that is strongly absorbed     

Magnetic spectra of ferrites under different external effects

The interrelation of magnetic spectra of polycrystalline manganese-zinc ferrites with the magnetic state of the material is investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 15–17, December, 1986.