Mössbauer spectra of a paramagnetic ion in an axial crystal field in the presence of spin-lattice relaxation

The influence of spin-lattice relaxation on the Mössbauer hyperfine spectra of the Fe³⁺ ion is investigated in the case of an axial crystal field. All the various influences of the relaxation process on the spectra can be explicitly described using two relaxation parameters. A detailed analysis of the Mössbauer relaxation spectra for the various temperatures, relations between the relaxation parameters and external magnetic field directions is carried out. When the magnetic field direction is nearly collinear with the symmetry axis and one of the relaxation parameters is small, the dynamics of Mössbauer spectra is shown to have anomalous features. The influence of random magnetic fields is shown to give an unconventional development of patterns as a function of the relaxation parameters.     

Ultrawide frequency linewidth of the permeability spectra of FeCoN thin film sputtered on the flexible substrate

Analysis shows that it is possible to make use of dispersed magnetic ripple fields to obtain a wide frequency linewidth of permeability spectra of soft magnetic thin films. As-sputtered FeCoN thin film sputtered on flexible Kapton substrate is studied as an example. It has ultrawide frequency linewidths of its resonance peaks in the permeability spectra, compared to its counterpart deposited on Si substrate. The frequency linewidth of FeCoN on Kapton substrate decreases with external magnetic field, showing a different field dependence from that of FeCoN on Si substrate. The ultrawide frequency linewidth and its decrease with external magnetic field are ascribed to the dispersed magnetic ripple fields caused by the flexible substrate. This work shows that the flexible substrate is effective in obtaining a wide frequency linewidth of the permeability spectra of soft magnetic thin films.     

Influence of the magnetic field strength and excitation intensity on the shape of microphotoluminescence spectra of quantum-well structures based on GaN/InGaN doped with Sm and Eu + Sm

This paper presents the results of complex measurements of the microphotoluminescence spectra of quantum-well structures based on InGaN/GaN〈Sm〉 and the determination of the concentration and charge state of the Sm dopant. It has been shown that an increase in the magnetic field strength and the excitation intensity of the microphotoluminescence spectra leads to an increase in the luminescence intensity and a shift in the position of the maximum of the emission wavelength toward the short-wavelength region of the spectrum. Measurements of the microphotoluminescence spectra with variations in the external magnetic field strength, as well as with the introduction of paramagnetic and magnetic impurities, provide additional information on the mechanisms of formation of luminescence spectra in the quantum-well structures InGaN/GaN〈Sm〉,〈Eu + Sm〉. In the long-wavelength region, the influence of the magnetic field on the shape of the microphotoluminescence spectra of the InGaN/GaN structures doped with Sm and Sm + Eu is less pronounced than that in the short-wavelength region.     

紫外分光光度法在检测磁化效果中的应用

用紫外分光光度法对几种物质分别作了经前后的吸收光谱,发现物质受磁化后其吸收峰的位置不变,但吸收强度发生了不同程度的变化,而且不同的磁化时间有不同的磁化效果。     

Features of two-photon resonances of nonlinear magnetooptical rotation of the plane of polarization for the initial population of fine-structure levels in alkali atoms

The features of nonlinear magnetooptical effects of fine-structure levels of an alkali atom, including effects in strong magnetic fields, as well as under conditions of two-photon resonance, are considered. The spectra of magnetooptical rotation and of magnetic circular dichroism have been obtained for the first time for the nontrivial initial population of magnetic sublevels of excited electronic states of an alkali atom, as well as under conditions of two-photon resonance. The decrease in the amplitude of resonances of initially populated fine-structure levels is explained by population transfer, taking place in strong fields. This transfer affects the rotation of the plane of polarization. The lower the initial population, the more pronounced the population transfer. Numerical experiments have shown that analysis of the resonance shapes in the spectra of magnetooptical rotation can yield information on the initial population of magnetic sublevels of excited electronic states of atoms.     

Polarization Phenomena in Transparency and Absorption Effects Induced by the Field of Unidirectional Waves

Physical processes that form the spectra of saturated absorption and magnetic scanning resonances on an atomic transition with level momentum J = 1 in the field of unidirectional waves of arbitrary intensity under variation in their polarization directions are investigated by numerical simulation and analytically. It is shown that anomalies in nonlinear resonance spectra are determined by the polarization of the waves and the degree of openness of the atomic transition, while anomalies in the experimentally observed magnetic scanning spectra are attributed to the magnetic coherence induced by the fields directly on the levels of the lower state, rather than to its transfer from the excited states, as was assumed earlier.     

On the advantages and validity of the method of decomposition of Mössbauer spectra from amorphous and disordered magnetic materials

A method for decomposition of Mössbauer spectra of amorphous and disordered magnetic materials is tested. Its algorithm is discussed as well as the adaptation of the method for processing of more complex spectra including correlation between the isomer shift and the magnetic hyperfine field and also quadrupole effect.     

Crystallographically-based analysis of the NMR spectra of maghemite

All possible iron environments with respect to nearest neighbour vacancies in vacancy-ordered and vacancy-disordered maghemite have been evaluated and used as the foundation for a crystallographically-based analysis of the published NMR spectra of maghemite. The spectral components have been assigned to particular configurations and excellent agreement obtained in comparing predicted spectra with published spectra taken in applied magnetic fields. The broadness of the published NMR lines has been explained by calculations of the magnetic dipole fields at the various iron sites and consideration of the supertransferred hyperfine fields.     

Localization of Dirac-like excitations in graphene in the presence of smooth inhomogeneous magnetic fields

The present paper discusses magnetic confinement of the Dirac excitations in graphene in the presence of inhomogeneous magnetic fields. In the first case a magnetic field directed along the z axis whose magnitude is proportional to 1/r is chosen. In the next case we choose a more realistic magnetic field which does not blow up at the origin and gradually fades away from the origin. The magnetic fields chosen do not have any finite/infinite discontinuity for finite values of the radial coordinate. The novelty of the two magnetic fields is related to the equations which are used to find the excited spectra of the excitations. It turns out that the bound state solutions of the two-dimensional hydrogen atom problem are related to the spectra of graphene excitations in the presence of the 1/r (inverse-radial) magnetic field. For the other magnetic field profile one can use the knowledge of the bound state spectrum of a two-dimensional cutoff Coulomb potential to dictate the excitation spectra of graphene. The spectrum of the graphene excitations in the presence of the inverse-radial magnetic field can be exactly solved while the other case cannot be. In the later case we give the localized solutions of the zero-energy states in graphene.     

On the shape of the gamma resonance spectra of slowly relaxing nanoparticles in a magnetic field

A nonstandard shape of the gamma resonance spectra of nanoparticles in the form of inverted five-step pedestal has been predicted, observed, and analytically described. This shape corresponds to the limit of high temperatures and slow relaxation of the homogeneous magnetization of single-domain particles with axial magnetic anisotropy. To describe the Mössbauer spectra of the ensemble of chaotically oriented nanoparticles in a magnetic field, a continual magnetic-dynamics model has been developed in the limit of slow relaxation. This model adequately describes the polarization effects observed in the experimental absorption spectra. The revealed features significantly expand the methodical capabilities of Mössbauer spectroscopy for the diagnostics of magnetic nanomaterials.     

Collapse in the Stoner-Wohlfarth noninteracting-particle model

A theory of Mössbauer spectra of noninteracting Stoner-Wohlfarth (SW) particles interacting with rf magnetic fields is developed. The theory makes it possible to calculate the absorption spectra for arbitrary frequency and amplitude of the rf field. The main features of the Stoner-Wohlfarth model are discussed. The Liouville superoperator formalism is used to generalize the results to the case of arbitrarily time-varying hyperfine fields at a nucleus. To understand the qualitative features of the collapse effect that are observed in the Mössbauer spectra of SW particles the particular case of a circularly polarized hyperfine field is studied, and an analytical expression is obtained describing the Mössbauer spectra for this case. An analysis is also made for weak rf magnetic fields and in this case the resonance behavior of the Mössbauer lines is traced as a function of the frequency of the rf field.     

Studying Specific Features of the Resonance Structure of the Background Noise Spectrum in the Frequency Range 1–10 Hz with Allowance for the Slope of the Earth’s Magnetic Field

We present new data on midlatitude features of the resonance structure of the magnetic ultralow-frequency noise spectrum in the frequency range 0.1–10 Hz, namely, the different frequency scale and frequency shift of the resonance-structure maxima for the East-West and North-South components. Resonance spectra of the magnetic components and polarization parameter of magnetic noise for the plane-stratified ionosphere model are numerically simulated with allowance for the inclination of the Earth's magnetic field on the basis of the International Reference Ionosphere IRI-2001 standard. Dependence of the calculated parameters of the resonance structure in the magnetic-component spectra on the source direction and inclination angle of the Earth's magnetic field is explored. The calculations make it possible to explain the different behavior of resonant oscillations in the linear-component spectra and the features of the resonance structure in the background-noise polarization parameter. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 7, pp. 575–584, July 2008.     

Temporal and preparation effects in the magnetic nanoparticles of Apis mellifera body parts

Magnetic nanoparticles in the Apis mellifera abdomens are well accepted as involved in their magnetoreception mechanism. The effects of sample preparation on the time evolution of magnetic particles in the honeybee body parts (antennae, head, thorax and abdomen) were investigated by Ferromagnetic Resonance (FMR) at room temperature (RT), for about 100 days. Three preparations were tested: (a) washed with water (WT); (b) as (a), kept in glutaraldehyde 2.5% in 0.1 M cacodylate buffer (pH 7.4) for 24 h and washed with cacodylate buffer (C); (c) as (a), kept in glutaraldehyde 2.5% for 24 h and washed with glutaraldehyde 2.5% in cacodylate buffer (GLC). The four body parts of young and adult worker presented magnetic nanoparticles. The Mn²⁺ lines are observed except for the antennae spectra. The high field (HF) and low field (LF) components previously observed in the spectra of social insects, are confirmed in these spectra. The HF line is present in all spectra while the LF is easily observed in the spectra of the young bee and it appears as a baseline shift in spectra of some adult parts. The HF intensity of the abdomen is commonly one order of magnitude larger than any other body parts. This is the first systematic study on the conservation of magnetic material in all body parts of bees. The results show that the time evolution of the spectra depends on the body part, conserving solution and bee age. Further measurements are necessary to understand these effects and extend it to other social insects.     

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)     

Optical pumping of the Zeeman components in the rubidium vapor

We investigated the optical pumping of the Zeeman components of rubidium atoms, in the presence of the external magnetic field ranging from the geomagnetic up to 130 Gauss. Using the saturated absorption spectroscopy with linearly polarized pump and probe laser beams, the rubidium Doppler-free spectra at different magnetic field strengths were measured. The dips (negative intensity signals) in the saturated absorption spectra of the ⁸⁷Rb hyperfine transition lines were observed. They come as a result of the alignment process induced by the incoherent population transfer due to the hyperfine optical pumping. By inspection of the dips for different magnetic field strengths we were able to conclude about the dynamics of the alignment process in the external magnetic field. Present work is a part of the investigations concerning the influence of the magnetic field on the velocity selective optical pumping of the rubidium atoms induced by femtosecond frequency comb [D. Aumiler, T. Ban, H. Skenderovi?, G. Pichler, Phys. Rev. Lett. 95 (2005) 233001; T. Ban, D. Aumiler, H. Skenderovi?, G. Pichler, Phys. Rev. A 73 (2006) 043407].     

A Manifestation of two-quantum transitions in the ODEPR spectra of the spin-correlated radical pairs in micelles

Optically detected electron paramagnetic resonance spectra of the spin-correlated radical pairs diffusing inside a spherical region are numerically simulated taking into account an exchange interaction between partners of the pairs. It is shown that these spectra contain the lines induced by the two-quantum transitions. The shape and the width of this two-quantum transition line are analyzed as depending on magnetic resonance parameters, on molecular kinetic parameters and chemical reactivity of radicals.     

Electron magnetic resonance of synthetic goethite in the range of the magnetic transition

Physics of the Solid State - The X-band electron magnetic resonance spectra of synthetic goethite have been investigated in the range of the magnetic phase transition. In addition to relatively...     

Study of local magnetic fields and magnetic ordering in fluid and solid matrices containing magnetite nanoparticles using TEMPOL stable radical

The stable nitroxide radical 2,2,6,6-tetramethyl-4-hydroxy-piperidin-1-oxyl (TEMPOL) has been applied as a sensor to study magnetite nanoparticles both in water suspension and in dried gelatin films. g-values and line widths of ESR spectra of the probe were found to be sensitive to the local magnetic fields of magnetic nanoparticles. Calculated on the basis of the sensor ESR spectra, local magnetic fields are stipulated by linear aggregates of magnetite nanoparticles formed in applied outer magnetic fields and are significantly lower than local magnetic fields estimated from the static magnetic measurements data.     

The closed-orbit and the photoabsorption spectra of lithium atom in varying＇magnetic fields

Using a simple analytic formula from closed orbit theory, we have calculated the photoabsorption spectra of Li atom in different magnetic fields. Closed orbits in the corresponding classical system have also been obtained for B=5.96T.We demonstrate schematically that the closed orbits disappear gradually with the decrease of the magnitude of the magnetic field. This gives us a good method to control the closed orbits in the corresponding system by changing the magnetic field, and thus changing the peaks in the photoabaorption spectra. By comparing the photoabsorption spectra of Li atom with those of hydrogen case, we find the core-scattered effects play an important role in multi-electron Rydberg atoms.     

Measurement of the (14)N nuclear quadrupole resonance frequencies by the solid effect

(1)H-(14)N nuclear quadrupole double resonance using magnetic field cycling between high and low magnetic field and solid effect in the low magnetic field is analyzed in details. The transition probabilities per unit time for the solid-effect transitions are calculated. The double resonance spectra are calculated in the limiting cases of fast and slow nitrogen spin-lattice relaxation. The double resonance spectra are measured in histamine and quinolinic acid. The experimental spectra are analyzed and the (14)N NQR frequencies are determined.