Zeeman Patterns Research Articles

Crystal-field Paschen-Back effect on ruby in ultrahigh magnetic fields

Zeeman spectra of the R lines of ruby (Cr$^{3+}$: $\alpha$-Al$_{2}$O$_{3}$) were studied in ultrahigh magnetic fields up to 230 T by magneto-photoluminescence measurements. The observed Zeeman patterns exhibit nonlinear behaviors above 100 T, evidencing the breakdown of the previously reported Paschen-Back effect for ${\bf B} \perp c$ geometry. We adopted the crystal-field multiplet theory including the cubic crystal field (${\mathcal H}_{\rm cubic}$), the trigonal crystal field (${\mathcal H}_{\rm trig}$), the spin-orbit interaction (${\mathcal H}_{\rm SO}$), and the Zeeman interaction (${\mathcal H}_{\rm Z}$). It is found that the nonlinear splitting of the R lines is owing to the hybridization between the $^{2}E$ and $^{2}T_{1}$ states, which leads to the quantization of these Zeeman levels with the orbital angular momentum. Our results suggest that the exquisite energy balance among ${\mathcal H}_{\rm cubic}$, ${\mathcal H}_{\rm trig}$, ${\mathcal H}_{\rm SO}$, and ${\mathcal H}_{\rm Z}$ realized in ruby offers a unique opportunity to observe the onset of the $crystal-field$ Paschen-Back effect toward the high-field extreme.

Magnetic hyperfine interactions in a sawtooth chain iron oxoselenite Fe2O(SeO3)2: Experimental and theoretical Investigation

The iron oxoselenite Fe2O(SeO3)2 hosts unique tilted saw-tooth chains of vertex-sharing iron triangles. It experiences long-range magnetic order below TN ≈ 105 K characterized by a sharp dichotomy in zero-field-cooled and field-cooled behavior (T < TN). The spin-flop transition at low temperatures, BSF = 5.5 T at T = 2 K, suggests the predominance of antiferromagnetic interactions. The 57Fe Mössbauer spectra at T » TN confirm the presence of three non-equivalent crystal sites for high-spin Fe3+ ions. Below TN, the well-resolved Zeeman patterns demonstrate a commensurate magnetic ordering in iron sublattices. The anomalously low value of the saturation hyperfine fields Bhf,Fei at 57Fe nuclei is discussed in terms of the spin reduction (<ΔS> ≈ 0.31), which results from a spin-wave treatment. The mean-field analysis of the temperature evolution of the fields Bhf,Fei(T) allowed evaluation of exchange interactions between different iron sublattices. A spin relaxation behavior of Fe2O(SeO3)2 in the temperature range T* < T < TN (T* ≈ 90 K), which is characteristic for frustrated systems, was shown by the Mössbauer measurements. Density functional theory (DFT) calculations provide the values of exchange parameters within and between the saw-tooth chains.

Circumstellar molecular maser emission of AGB and post-AGB stars

AbstractResults of long-term studies of circumstellar molecular maser emission of late-type giant and supergiant variable stars are reported. In the 1.35-cm H2O line, the peak flux density correlates with the optical brightness lagging behind it by 0.3–0.4 P (P is the stellar period). “Superperiods” of 10 to 15 P are visible in several stars, demonstrated as high maxima in the visible light curve and associated flares in the H2O maser line. In the 18-cm OH lines, full polarization of the maser emission has been measured. Variable Zeeman patterns suggesting a changing magnetic field of a few milligauss have been detected.

Thermodynamic Properties, Mössbauer Study, and First-Principles Calculations of TlFe(MoO4)2

We report the results of magnetization and specific heat measurements, a 57Fe Mössbauer study of hyperfine interactions and density functional theory calculations in TlFe(MoO4)2 demonstrating two magnetic phase transitions at TN2 = 5.7 K and TN1 = 6.2 K. In the asymptotical critical region TN2 ≤ T ≤ TN1, the temperature dependence of the average hyperfine magnetic field ⟨Bhf(T)⟩ at the 57Fe nuclei is well-described by the power law ⟨Bhf(T)⟩ ∝ tβ with the static critical exponent β ≈ 0.37 inherent for a three-dimensional magnet. In this range, the Mössbauer spectra are described in terms of collinear spin-density-wave with the inclusion of high-order harmonics. The spectra of the low-temperature phase, below TN2, are well-fitted by a single six-line Zeeman pattern reflecting the equivalence of magnetic sites occupied by Fe3+ ions in an antiferromagnetic structure. The first-principles calculations allowed estimation of the strength of main exchange interactions.

Sun-sized Water Vapor Masers in Cepheus A

Abstract We present the first VLBI observations of a Galactic water maser (in Cepheus A) made with a very long baseline interferometric array involving the RadioAstron Earth-orbiting satellite station as one of its elements. We detected two distinct components at −16.9 and 0.6 km s−1 with a fringe spacing of 66 μas. In total power, the 0.6 km s−1 component appears to be a single Gaussian component of strength 580 Jy and width of 0.7 km s−1. Single-telescope monitoring showed that its lifetime was only eight months. The absence of a Zeeman pattern implies the longitudinal magnetic field component is weaker than 120 mG. The space–Earth cross power spectrum shows two unresolved components smaller than 15 μas, corresponding to a linear scale of 1.6 × 1011 cm, about the diameter of the Sun, for a distance of 700 pc, separated by 0.54 km s−1 in velocity and by 160 ± 35 μas in angle. This is the smallest angular structure ever observed in a Galactic maser. The brightness temperatures are greater than 2 × 1014 K, and the line widths are 0.5 km s−1. Most of the flux (about 87%) is contained in a halo of angular size of 400 ± 150 μas. This structure is associated with the compact H ii region HW3diii. We have probably picked up the most prominent peaks in the angular size range of our interferometer. We discuss three dynamical models: (1) Keplerian motion around a central object, (2) two chance overlapping clouds, and (3) vortices caused by flow around an obstacle (i.e., von Kármán vortex street) with a Strouhal number of about 0.3.

Revised Landé gJ-factors of some 141Pr II levels using collinear laser ion beam spectroscopy

The Zeeman effect of singly ionized praseodymium spectral lines was studied at small magnetic fields up to 334G, using the high-resolution spectroscopic method of collinear laser-ion-beam spectroscopy (CLIBS), where a collimated fast ion beam is superimposed with a counter propagating laser beam tuned to the desired transition. This nearly Doppler-effect-free technique enables to observe linewidths as low as 100MHz and thus to record the Zeeman patterns of the hyperfine structure of the investigated spectral lines.From the Zeeman patterns of 21 lines of Pr II lines in the range 570.45–609.038nm we have re-determined the Landé gJ-factors of 14 levels of the f3dodd and 16 levels of the f3p and f2d2even configurations.The obtained experimental Landé factors are compared with available earlier measurements as well as with theoretical calculations.

Helical magnetic structure and hyperfine interactions in FeP studied by 57Fe Mössbauer spectroscopy and 31P NMR

We report results of 57Fe Mössbauer and 31P NMR studies of a phosphide FeP powder sample performed in a wide temperature range including the point (TN ≈ 120 K) of magnetic phase transitions. The 57Fe Mössbauer spectra at low temperatures T < TN present a very complex Zeeman pattern with line broadenings and sizeable spectral asymmetry. It was shown that the change of the observed spectral shape is consistent with the transition into a space-modulated helicoidal magnetic structure. Analysis of the experimental spectra was carried out assuming an anisotropy of the magnetic hyperfine field Hhf at the 57Fe nuclei when the Fe3+ magnetic moment rotates with respect to the principal axis of the electric field gradient (EFG) tensor. The obtained large temperature independent anharmonicity parameter m ≈ 0.96 of the helicoidal spin structure results from easy-axis anisotropy in the plane of the iron spin rotation. It was assumed that a very low maximal value of Hhf(11 K) ≈ 36 kOe and its high anisotropy ΔHanis(11 K) ≈ 30 kOe can be attributed to the stabilization of iron cations in the low-spin state (SFe = 1/2). The 31P NMR measurements demonstrate an extremely broad linewidth reflecting the spatial distribution of the transferred internal magnetic fields of the Fe3+ ions onto P sites in the magnetically ordered state.

Zeeman effect of hyperfine-resolved spectral lines of singly ionized praseodymium using collinear laser–ion-beam spectroscopy

Using the high-resolution spectroscopic method of collinear laser--ion-beam spectroscopy (CLIBS), the Zeeman effect of singly ionized praseodymium spectral lines has been studied at relatively small magnetic fields up to 330 G. With this unusual method for studying the Zeeman effect of ionic lines we recorded Zeeman-hyperfine structure patterns with clearly resolved components with linewidths as low as 60 MHz, which is only sometimes the natural linewidth. From the Zeeman patterns of 30 lines, improved Land\'e ${g}_{J}$ factors were determined for 39 Pr ii levels of the $4{f}^{3}5d$, $4{f}^{2}5{d}^{2}$, and $4{f}^{3}6p$ configurations.

Determination of Landé factors in the F4Δ5/2,7/2 state of 56FeH by laser excitation spectroscopy

This paper provides a set of effective Landé factors gJ for the first rotational levels of vibrational levels 0 and 1 of the F4Δ state of FeH, obtained from analysis of partially-resolved Zeeman patterns recorded in laser excitation, working at magnetic fields between 2000 and 5000Gauss.

Measuring the surface magnetic fields of magnetic stars with unresolved Zeeman splitting

High-dispersion, archival spectra of magnetic Ap stars with resolved Zeeman components in Stokes I are used to derive a simple relation that can be utilised to estimate the mean surface field strengths of stars with v sin i > 10 km/s. For each star, the mean surface field, as measured from the observed splitting in Fe II at 6149 A, is compared to the differential broadening of spectral lines with large and small Lande factors in order to produce a relation to estimate the field strengths of magnetic stars with unresolved Zeeman patterns. The method is shown to be reliable for rotational velocities up to about 50 km/s for field strengths down to about 5 kG. These results should allow for better constraints to be placed on the mean surface magnetic fields of Ap stars where Zeeman patterns are unresolved.

Parkes full polarization spectra of OH masers – II. Galactic longitudes 240° to 350°

Full polarization measurements of 1665 and 1667-MHz OH masers at 261 sites of massive star formation have been made with the Parkes radio telescope. Here we present the resulting spectra for 157 southern sources, complementing our previously published 104 northerly sources. For most sites, these are the first measurements of linear polarization, with good spectral resolution and complete velocity coverage. Our spectra exhibit the well-known predominance of highly circularly polarized features, interpreted as $\sigma$ components of Zeeman patterns. Focusing on the generally weaker and rarer linear polarization, we found three examples of likely full Zeeman triplets (a linearly polarized $\pi$ component, straddled in velocity by $\sigma$ components), adding to the solitary example previously reported. We also identify 40 examples of likely isolated $\pi$ components, contradicting past beliefs that $\pi$ components might be extremely rare. These were recognised at 20 sites where a feature with high linear polarization on one transition is accompanied on the other transition by a matching feature, at the same velocity and also with significant linear polarization. Large velocity ranges are rare, but we find eight exceeding 25 km/s, some of them indicating high velocity blue-shifted outflows. Variability was investigated on timescales of one year and over several decades. More than 20 sites (of 200) show high variability (intensity changes by factors of four or more) in some prominent features. Highly stable sites are extremely rare.

On the spectropolarimetric signature of FeH in the laboratory and in sunspots

RésuméLaboratory spectra showing Zeeman patterns in some FeH lines susceptible to be used as magnetic probes in cool stellar atmostpheres have been recorded in the laboratory, and molecular Landé factors obtained from analysis. These Landé factors have been used to model some lines recorded in Stokes V polarisation in sunspot spectra at the solar telescope THEMIS.

Resolved fluorescence spectra of NiH. Electronic structure, electronic energy transfer, and the Zeeman effect in low-lying states

Fourier transform spectra of collisionally induced fluorescence following isotopically selective laser excitation of NiH at ∼550 nm have located an excited Ω = 1/2 state of NiH lying 17900 cm−1 above the electronic ground state. This is identified as v = 0 of a 2Π1/2 state originating from an Ni+ 3d84s1 2F configuration. Emission from this Ω′ = 1/2 state occurs predominantly to v″ = 0 and 1 of the 2Σ+ and W2 2Π1/2 ligand field states, locating elusive f parity levels of W2 2Π1/2 up to 5600 cm−1 above the first rotational level of the electronic ground state, X 1 2Δ5/2. Collisionally induced fluorescence following laser excitation at lower energies has also been recorded in the presence of a magnetic field (0.7–1 T), at Doppler limited resolution. Effective Landé factors g J for rotational levels of the v = 0 and 1 levels of the low-lying Ω″ = 5/2 and 3/2 components of the 2Δ and 2Π states of NiH have been derived from partially resolved Zeeman patterns. About 1600 transitions recorded in field-free conditions have been reduced to term energies relative to the lowest level of the ground state. They confirm strong spin-orbit mixing between the low-lying ligand-field states.

Characterization of anomalous Zeeman patterns in complex atomic spectra

The modeling of complex atomic spectra is a difficult task, due to the huge number of levels and lines involved. In the presence of a magnetic field, the computation becomes even more difficult. The anomalous Zeeman pattern is a superposition of many absorption or emission profiles with different Zeeman relative strengths, shifts, widths, asymmetries, and sharpnesses. We propose a statistical approach to study the effect of a magnetic field on the broadening of spectral lines and transition arrays in atomic spectra. In this model, the $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ profiles are described using the moments of the Zeeman components, which depend on quantum numbers and Land\'e factors. A graphical calculation of these moments, together with a statistical modeling of Zeeman profiles as expansions in terms of Hermite polynomials are presented. It is shown that the procedure is more efficient, in terms of convergence and validity range, than the Taylor-series (TS) expansion in powers of the magnetic field, which was suggested in the past. Finally, a simple approximate method to estimate the contribution of a magnetic field to the width of transition arrays is proposed. It relies on our recently published recursive technique for the numbering of $LS$ terms of an arbitrary configuration.

Description of anomalous Zeeman patterns in stellar astrophysics

The influence of a magnetic field on the broadening of spectral lines and transition arrays in complex spectra is investigated. The anomalous absorption or emission Zeeman pattern is a superposition of many profiles with different relative strengths, shifts, widths, asymmetries and sharpnesses. The "sigma" and "pi" profiles can be described statistically, using the moments of the Zeeman components. We present two statistical modellings: the first one provides a diagnostic of the magnetic field and the second one can be used to include the effect of a magnetic field on simulated atomic spectra in an approximate way.

A Study on the Properties of Substituted Ferrite (Fe-Al-Ga-Si)

Abstract The crystal structure and magnetic properties of a new solid solution type ferrite (Fe 2 O 3 ) 5 -(Al 2 3 3.4 -(Ga 2 3 0.6 -SiOwere investigated using X-ray diffraction and Mossbauer spectroscopy. The results of the X-ray diffraction pattern indicated thatthe crystal structure of the sample appears to be a cubic spinel type structure. The lattice constant (a = 8.317 A) decreasesslightly with the substitution of Ga 2 O 3 even though the ionic radii of the Ga ions are larger than that of the Al ions. The resultscan be attributed to a higher degree of covalency in the Ga-O bonds than in the Al-O and Fe-O bonds, which can also beexplained using the observed Mossbauer parameters, which are the magnetic hyperfine field, isomer shift, and quadrupolesplitting. The drastic change in the magnetic structure according to the Ga ion substitution in the (Fe 2 O 3 ) 5 (Al 2 O 3 ) 4-x (Ga 2 O 3 ) x SiOsystem and the low temperature variation have been studied through a Mossbauer spectroscopy. The Mossbauer spectrum atroom temperature shows the superpositions of two Zeeman patterns and a strong doublet. It shows significant departures fromthe prototypical ferrite and is comparable with the diluted ferrite. The doublet of spectrum at room temperature appears tooriginate from superparamagnetic clusters and also the asymmetry of the doublet appears to be caused by the preferredorientation of the crystallites. The Mossbauer spectra below room temperature show various complicated patterns, which canbe explained by the freezing of the superparamagnetic clusters. On cooling, the magnetic states of the sample were various andmulti critical. Key words nonstoichiometric ferrite, superparamagnetic clusters, Zeeman pattern, Mossbauer spectroscopy, X-ray diffraction.

Magnetic properties of Ni–Cu–Mn ferrite system

Three groups according to the substitution of Cu 2+ and Mn 3+ in the system Ni 1− x Cu x Fe 2− y Mn y O 4 ferrite with x = 0.2, 0.5, 0.8, and y varying from 0.0 to 1.0 in steps of 0.25 are prepared by solid state reactions. The phases of the Ni 1− x Cu x Fe 2− y Mn y O 4 ferrite have been confirmed by X-ray diffraction (XRD). The results demonstrate that all of the synthesized materials are spinel with cubic unit cell and the lattice constant increased with increases of the Cu and Mn ions for all samples. The hyperfine interaction was studied by the Mössbauer spectroscopy at room temperature for all samples. The spectra of all samples show two well-resolved Zeeman patterns corresponding to A- and B-sites. The hyperfine field decreases with increasing Cu and Mn ions concentration. The Curie temperature, T C, was calculated from the temperature dependence of magnetization curves. The hysteresis curve recorded at room temperature shows that the samples are ferrimagnetic materials. The cation distribution was estimated from the results of Mössbauer spectroscopy and magnetic measurements.

Polarized atomic radiative emission in electric and magnetic fields1This article is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas.

A reduced density matrix approach is employed to provide a general theoretical description of polarized radiative emission during single-photon transitions from bound and auto-ionizing states of many-electron atomic systems in the presence of a general arrangement of static (or quasi-static) electric and magnetic fields. Polarized radiative emission from partially ionized atomic systems can occur as a result of the excitation of the radiating atomic states by electrons or ions with an anisotropic velocity distribution, which can be produced in an electron or ion beam experiment, and in a non-equilibrium plasma environment. Polarized radiative emission can also be produced or modified during the excitation of the atomic system in the presence of electric and magnetic fields, and electromagnetic fields. In electric and magnetic fields, the normally overlapping angular momentum projection components of atomic spectral lines can be substantially shifted from their field-free positions and split into spectroscopically resolvable (and inherently polarized) features. Because of the breakdown of the field-free angular momentum and parity selection rules, otherwise forbidden components of atomic spectral lines can be generated. Using a representation based on the field-free many-electron atomic states, the Stark–Zeeman patterns can be determined by a diagonalization of the atomic Hamiltonian in the presence of electric and magnetic fields. In the density operator approach, account can be taken of the coherent excitation of a particular subspace of the initial atomic bound or auto-ionizing states. A general expression for the matrix elements of the detected-photon density operator is obtained and provides a unified framework for the analysis of the spectral intensity, angular distribution, and polarization of the Stark–Zeeman patterns. From a unified development of time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations of the more comprehensive reduced density matrix approach, the non-equilibrium atomic state kinetics and the homogeneous spectral line shapes can be systematically and self-consistently described.

Synthesis, structural and electrical characterization of Sb 3+ substituted spinel nickel ferrite (NiSb xFe 2− xO 4) nanoparticles by reverse micelle technique

Spinel nickel ferrite with nominal composition NiFe 2− x Sb x O 4 (where x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1) has been synthesized by the reverse microemulsion method. The samples synthesized were characterized by XRD, FTIR, TGA/DTGA, SEM, AFM, Mossbauer Spectroscopy and DC electrical resistivity measurements. The XRD analysis confirmed the formation of single spinel phase and the crystallite size was found to be in the range of 8–38 nm. The particle size of the synthesized samples was also confirmed by the AFM and SEM which was found in the range of 5–45 nm and 10–45 nm, respectively and this size is small enough for obtaining the suitable signal-to-noise ratio in high density recording media. The Mossbauer spectra of samples showed two well-resolved Zeeman patterns corresponding to A and B sites and also observed a doublet at higher substitution. The DC electrical resistivity showed an interesting behavior with temperature and observed a metal-to-semiconductor transition temperature ( T M–S) which suggests that the material can be applied for switching applications. The resistivity increases with the increase in Sb-content and it suggests that the material can be fruitfully used for applications in microwave devices.

Polarization observations of the OH maser W75N on the Nançay radio telescope

Results of observations of the OH maser in W75N at 18 cm are reported. The observations were obtained on the radio telescope of the Nancay Radio Astronomy Observatory (France) from October 2007 to April 2009. The profiles of the Stokes parameters I, Q, U, and V in the 1665 and 1667 MHz OH lines have been measured. A technique taking into account instrumental polarization has been developed and applied. The emission in the OH lines is strongly polarized both linearly and circularly. The degree of polarization of some emission features reaches almost 100%. There were two flares of the maser emission in 2008–2009. During a flare at a radial velocity of +5.5 km/s, a Zeeman pattern was detected in the 1667 MHz line. The measured intensity of the line-of-sight component of the magnetic field was −1.1 mG, which corresponds to the field being directed away from the observer. The maser flares and the associated enhancement of the magnetic field could be associated with the compression of gas at a shock front.