Splitting of NMR signals in parallel fields in the easy-plane antiferromagnet FeBO3

Experimental observations are reported of the splitting of NMR lines of ⁵⁷Fe into two absorption peaks in a static magnetic field H ₀ parallel to a variable field H ₁ in the basis plane. The field dependence of the intensity and the variation in the resonance frequencies of the absorption peaks with H ₀ are studied. These results can be used to explain some features of the layered domain structure of iron borate. Fiz. Tverd. Tela (St. Petersburg) 41, 290–292 (February 1999)     

New polaron effect in magnetooptic phenomena in a quantum well

It is predicted that resonance coupling between two discrete electron energy levels corresponding to different size-quantization quantum numbers and different Landau quantum numbers can occur in a quantum well in a quantizing magnetic field. The resonance coupling is due to the interaction of an electron with LO phonons and results in the formation of polaron states of a new type. It is shown that for a certain value of the magnetic field, which depends on the splitting of the electron size-quantization levels, the absorption peak and the two-phonon resonance Raman scattering peak split into two components, the separation between which is determined by the electron-phonon coupling constant. The resonance coupling between size-quantization levels with the same Landau quantum numbers is also studied. The splitting of the peaks in this case is virtually independent of the magnetic field and can be observed in much weaker fields. The experimental observation of the effect will make it possible to determine the relative position of the electronic levels and the electron-phonon coupling constant. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 511–515 (10 April 1997)     

Influence of the impurity scattering on the absorption of electromagnetic radiation by anisotropic quantum dots

The absorption of electromagnetic radiation by quantum dots is investigated taking into account the processes related to simultaneous scattering from ionized impurities. It is shown that even a single impurity leads to additional resonance peaks. The positions of resonance peaks are determined. The effect of magnetic field on the absorption in dots is studied. The relative intensity of the resonance peaks is analyzed.     

Electrodynamic response of a nanosphere placed in a magnetic field

Absorption of electromagnetic radiation by 2D electrons at the surface of a quantum sphere placed in a weak magnetic field is studied. It is shown that at low temperatures, the absorption curve exhibits four resonance peaks observed in the Faraday geometry (photon wave vector parallel to the magnetic field) and six peaks in the Voigt geometry (photon wave vector perpendicular to the magnetic field). In the particular case of the Voigt geometry, where the photon polarization vector is parallel to the magnetic field, the absorption curve exhibits only two resonance peaks. The shape, position, and intensity of the peaks are examined. It is shown that at temperatures close to zero, steps of two types appear in the absorption curve. One type of steps is associated with crossing of the μ-?ω level by the electron energy levels, while steps of the other type arise when electron energy levels cross the chemical potential μ.     

Quantum waves in noble metals

A theoretical study is presented of the effect of hole energy quantization in a dc magnetic field on microwave penetration through a noble-metal plate. It is shown that quantization results in strong oscillations of cyclotron absorption. Between the absorption peaks, the damping decreases sufficiently to enable propagation of unique quantum waves. Excitation of such waves in a metallic plate gives rise to sharp oscillations of its surface resistance with magnetic field. The shape of these oscillations is also very unusual. Fiz. Tverd. Tela (St. Petersburg) 41, 1354–1360 (August 1999)     

Electrodynamic response of a nanosphere

The electrodynamic response of electron gas on the surface of a nanosphere in a weak magnetic field is studied. The case of the photon polarization vector oriented parallel to the magnetic field (the Faraday geometry) is considered. An analytic expression for the coefficient of electromagnetic-radiation absorption by the nanosphere is derived. It is shown that, at low temperatures, the absorption curve has, in the general case, two resonance peaks. The curve also exhibits breaks.     

Influence of spin–orbit interaction,Zeeman effect and light polarisation on the electronic and optical properties of pseudo-elliptic quantum rings under magnetic field

ABSTRACT

We theoretically investigated the influences of the magnetic field and light polarisation on the electronic and optical properties of a GaAs/GaAlAs pseudo-elliptic quantum ring, modelled by an outer ellipsis and an inner circle, in the presence of the Rashba and Dresselhaus spin–orbit interactions and Zeeman effect. We show that Aharonov-Bohm oscillations of the energy spectrum are not affected by the presence of the Zeeman effect alone but, in the presence of Rashba and Dresselhaus spin–orbit couplings, the periodicity of certain levels becomes hardly definite. The Zeeman effect generally enhances/diminishes the separation levels produced by Rashba/Dresselhaus interactions (SOI) and when both types of SOI are considered, the effect depends on their relative strength. The magnetic field can trigger spin-flip for each type of spin–orbit interaction and Zeeman effect or their combination through anticrossings in the energy spectra. Our results reveal that the absorption spectra are very sensitive to the magnetic field and light polarisation. For all polarisations considered, the magnetic field increment leads to the redshift or blueshift of some particular peaks (an effect of this ring geometry) and a better separation of the peaks. The x-polarised light determines spectra with many small, but separated peaks while the circular polarised light leads to spectra with large peaks of high amplitude.     

Stripe domains in Permalloy films as observed by ferromagnetic resonance and magnetic force microscopy

We have studied the static and dynamic responses of three (62, 115 and 308 nm thick) Permalloy (Ni_0.81Fe_0.19) films by DC magnetization, ferromagnetic resonance and magnetic force microscopy. The thickest film presents very regular stripe domains with widths slightly smaller than the film thickness. Ferromagnetic resonance performed on the thinnest film shows one absorption peak when the field is applied along the film plane, and more than one in the other samples. These multiple absorptions are analogous to the high frequency susceptibility peaks observed at zero field in Permalloy films above the critical thickness reported previously by other authors.     

Magnetoabsorption in n-type InSb from 8 to 15 μm

Magnetoabsorption measurements in n-type InSb at T?30K have been made between ～ 8 and 15 μm using magnetic fields up to 150 kOe. The observed absorption peaks are identified as due to combined resonance, harmonics of cyclotron resonance and the corresponding LO phonon-assisted resonances. These resonant absorptions are considered to be important in the interpretation of the observed magnetic field behavior of the threshold and output power of the InSb spin-flip Raman laser pumped with 10.6 μm CO₂ laser.     

Dynamics of flavin containing radical pairs in SDS micellar media probed by static and pulse magnetic field effect and pulse ADMR

ABSTRACT

The dynamics of the radical pairs generated from the electron transfer reaction from indole derivatives to flavin derivatives are studied by three techniques, time resolved magnetic field effect (TR-MARY) and pulse absorption detected magnetic resonance (ADMR), and absorption detected switching of external magnetic field techniques (AD-SEMF). The three techniques complementarily work for the precise analysis of the radical pair kinetics. The results by all three techniques reflect the difference of the hydrophobic nature of the radicals in the lifetime of RP in a micelle. Overcoming the difficulty of the determination of the short RP lifetime under the nearly quasi steady state due to slow and inhomogeneous decay kinetics of the precursor triplet excited state, AD-SEMF analysis enabled us to determine the kinetic parameters, which is consistent with the qualitatively observed by the other techniques.     

The influence of resonance IR laser radiation on magnetoabsorption in quantum wires

The coefficient of interband absorption of a weak electromagnetic wave by quantum wires in a transverse magnetic field and an intense laser radiation field is calculated. It is shown that, if the laser radiation frequency is equal either to the size quantization frequency (dimensional infrared resonance) or to a hybrid frequency (magnetoinfrared resonance), laser illumination can determine the shape of absorption oscillations. In particular, it is shown that the second magnetoabsorption peak is split into two peaks, the half-widths of which and the distance between which depend on the intensity of resonance laser radiation. The influence of the polarization of IR radiation on the interband absorption in quantum wires is discussed. The dynamics of the frequency dependence of the optical absorption coefficient with increasing intensity of resonance laser radiation is studied.     

Nonlinear waves in zinc

A theoretical analysis is made of Doppler-shifted cyclotron resonance in zinc in linear and nonlinear regimes. It is shown that the absence of a threshold for cyclotron absorption by holes makes the doppleron strongly damped or eliminates it for low-amplitude wave-fields. At high amplitudes capture of holes by the magnetic field of the wave suppresses collisionless absorption and the doppleron can propagate. As a result, the impedance of the plate is an oscillating function of the magnetic field. It is shown that the effect should be observed at frequencies of the order of a few tens of kilohertz, in magnetic fields of the order of a few kilogauss, and for exciting field amplitudes of the order of a few tens of gauss. Zh. éksp. Teor. Fiz. 114, 725–734 (August 1998)     

Spatial correlation of an electron and hole in quasi-two-dimensional electronic system in a strong magnetic field and its relationship to the light-scattering tensor

The spatial correlation of light-generated electrons and holes in a quasi-two-dimensional electron gas in a strong magnetic field is investigated in an approximation linear in the intensity of the exciting light. The correlation is due to the interaction of the electrons and holes with longitudinal optical (LO) phonons. The theory permits calculating, on the basis of a special diagrammatic technique, two distribution functions of an electron-hole pair with respect to the distance between the electron and the hole after the emission of N phonons: first, the function determining the total number of pairs which have emitted N phonons and, second, the function related to the rank-4 light-scattering tensor in interband resonance Raman scattering of light. A special feature of the system is that the electron and hole energy levels are discrete. The calculation is performed for a square quantum well with infinitely high barriers. The distribution function and the total number of electron-hole pairs before the emission of phonons as well as the distribution function corresponding to two-phonon resonance Raman scattering are calculated. The theory predicts the appearance of several close-lying peaks in the excitation spectrum under resonance conditions. The number of peaks is related to the number of the Landau level participating in the optical transition. The distance between peaks is determined by the electron-phonon coupling constant. Far from resonance there is one peak, which is much weaker than the peaks obtained under resonance conditions. Zh. éksp. Teor. Fiz. 111, 2194–2214 (June 1997)     

Angular dependence of the spin-wave resonance spectra in multilayer films

The angular dependence of the spin-wave resonance spectra is investigated in multilayer magnetic films in which the spin pinning mechanism changes from dynamical to dissipative. A fundamental difference is observed in the character of the angular dependences of the spectra for three-layer films as opposed to two-layer films. In particular, the number of peaks in the spectrum of three-layer films is observed to decrease and then increase twice as the angle between the magnetic field and the normal to the film is varied by π/2. Zh. Tekh. Fiz. 69, 97–101 (November 1999)     

Ballistic conductance of a quasi-one-dimensional microstructure in a parallel magnetic field

We discuss the behavior of the ballistic conductance of a quasi-one-dimensional microstructure in a parallel magnetic field when there is electron scattering by a single point impurity inside a channel. An exact analytic formula for the conductance is derived for a model in which the confinement potential is a parabolic well. We show that the conductance curve consists of quantization steps with sharp resonance peaks near the thresholds. Finally, we find the amplitudes and halfwidths of these peaks. Zh. éksp. Teor. Fiz. 111, 2215–2225 (June 1997)     

Balance-equation approach to terahertz-field-driven magnetotransport in semiconductors

We investigate the magnetotransport in semiconductors under the influence of a dc or slowly-varying electric field, an intense polarized radiation field of terahertz frequency, and a uniform magnetic field, being in arbitrary directions and having arbitrary strengths. Effective force- and energy-balance equations are derived by using a gauge that the magnetic field and the high-frequency radiation field are described by a vector potential and the dc or slowly-varying field by a scalar potential, and by distinguishing the slowly-varying velocity from the rapidly-oscillating velocity related to the high-frequency field. These equations, which include the elastic photon process and all orders of multiphoton absorption and emission processes, are applied to the examination of the effect of a terahertz radiation on the magnetophonon resonance of the longitudinal resistivity in the transverse configuration in nonpolar and polar semiconductors. We find that the previous zero-photon resonance peaks are suppressed by the irradiation of the terahertz field, while many new peaks, which may be related to multiphoton absorption and emission processes, emerge and can become quite distinct, at moderately strong radiation field. Received 17 May 1999     

Temperature anomalies in the nonlinear magnetoacoustic properties of manganese-zinc spinel single crystals

The absorption of a magnetoelastic wave and the nonlinear resonance interaction of counterpropagating magnetoelastic waves in a manganese-zinc spinel single crystal have been investigated near the conjectured spin-reorientational transition. The convolution signal vanishes near T _tr=291 K; this is explained by the relaxational dynamics of the magnetic mode near the transition. The increase in the strength of the field corresponding to the maximum of the convolution with decreasing temperature is explained by a change in the demagnetizing field. Fiz. Tverd. Tela (St. Petersburg) 39, 652–655 (April 1997)     

Confined-acoustic-phonon-assisted cyclotron resonance via multi-photon absorption process in GaAs quantum well structure

Phonon-assisted cyclotron resonance (PACR) in GaAs quantum well (QW) structure is investigated via multi-photon absorption process when electrons interact with the confined acoustic phonon through deformation potential. The additional peaks in the absorption spectrum due to transitions between Landau levels accompanied with the emission and absorption of phonons are indicated. The dependence of absorption power on the temperature, magnetic field and well width is presented. Using profile method, we obtain PACR-linewidth as profiles of the curves. The temperature, magnetic field and well width dependences of the PACR-linewidth are investigated. The results are compared with those in the case of mono-photon absorption process, as well as in the electron-bulk acoustic phonon interaction. The results show that the multi-photon absorption process is strong enough to be detected in PACR.     

Low field microwave absorption and magnetization process in CoFeNi electroplated wires

Ferromagnetic resonance （FMR）, Ferromagnetic antirresonance （FMAR） and low field magnetoimpedance （MI） are the characteristic features of high frequency losses in applied fields. While some results on FMR and FMAR in CoFeNi electroplated wires were reported earlier, here we present microwave absorption in CuBe wires electroplated by 1 μm FeCoNi magnetic layer at very low fields. These data are comparatively analysed together with longitudinal hysteresis loops in order to reveal the correlation between power absorption and magnetization processes. Microwave studies are made by using the cavity perturbation method at 9.65 GHz for a DC field parallel to the sample axis, and with microwave magnetic field hrf parallel or perpendicular to the wire axis. Two peaks have been observed in all samples, one is due to FMR, and the other is, at very low fields, related to MI. The MI peaks represent minima in power absorption. By comparing with the hysteresis loop we remark the close correspondence between the MI phenomena in the axial mode and the concomitant magnetization process.     

Anisotropy of the Resonance Transformation of the Microhardness of Crystals after Their Exposure in the EPR Scheme in the Earth’s Magnetic Field

It is shown that the preliminary exposure of ZnO, triglycine sulfate, and potassium hydrogen phthalate crystals in ultralow crossed magnetic fields—Earth’s magnetic field and ac pump field—leads to a resonance change in their microhardness. The resonance frequency of microhardness peaks is determined by the classical condition of electron paramagnetic resonance only at certain orientations of the crystals with respect to the Earth’s magnetic field B_Earth. Rotations of all samples with respect to the direction B_Earth by angle θ reduce the resonance frequency in proportion to cosθ. The observed anisotropy has been attributed to the presence of their own local magnetic fields B_loc ? B_Earth in the crystals.