The absorption,magnetic circular dichroism and emission of Eu2+ in cubic elpasolites

The absorption, magnetic circular dichroism (MCD) and emission/excitation spectra of some $\text{4?}{}^7\text{→4?}{}^6\text{5d}$ transitions in Eu²⁺ in several hexachloro and hexabromoelpasolites have been measured. Data were collected between 5 and 300 K and up to energies of 42,000 cm^?1. The absorption and MCD were satisfactorily interpreted using a coupling scheme that treats the d-electron crystal field as being much greater than the f-electron spin orbit coupling and essentially ignores other interactions.     

The absorption and magnetic circular dichroism of spectra of Cs2NaPrCl6

The room temperature absorption and magnetic circular dichroism spectra and the absorption spectrum at liquid helium (liquid He) temperature have been measured for Cs₂NaPrCl₆. At room temperature the crystal is cubic and the Pr³⁺ sites have O _h symmetry. All terms above 15 000 cm^-1, except ¹S₀, have been assigned and a previous assignment in PrCl₆ ^3- has been shown to be incorrect. The transition at 20 631 cm^-1 is assigned to ³H₄(A _1g ) →³P₁(T _1g ), in contradiction to previous assignments of Pr³⁺ spectra in other systems. A rich vibrational structure was observed in every transition. Vibrations have been assigned using the site group approximation and there is substantial agreement with the vibrational assignments in Cs₂NaEuCl₆. A crystal phase transition takes place between room temperature and liquid nitrogen temperature and the O _h forbidden transitions, A _1g →E_g and T _2g , are observed. At lower temperatures many additional lines are observed but it is unclear presently whether they are due to lower symmetry or a breakdown of the site group approximation.     

Near infrared absorption and magnetic circular dichroism in Zr-doped YIG

Near infrared absorption and MCD measurements are reported. The results show three transitions below the wavelength of 2.0μm, analogous to those previously observed on (Sn) YIG and a new one at 2.15 μm. The origin of these transition is related to the localization of the dopant ions.     

The electronic absorption and magnetic circular dichroism spectra of IrBr6 2- in several host crystals

The absorption and magnetic circular dichroism (M.C.D.) spectrum of the IrBr₆ ^2- ion at room and liquid helium temperature has been studied in the host crystals (NH₄)₂SnBr₆, K₂SnBr₆ and (C₂H₅NH₃)₂SnBr₆ in the region ～11 000–21 000 cm^-1. An interpretation of the spectrum is presented which differs significantly from those suggested previously. In order of increasing energy the allowed bands are assigned to the following ligand-to-metal charge-transfer transitions: E_g ″(² T _2g )→ U_u ′(² T _1u ) (13–14 000 cm^-1), E_g ″(² T _2g )→ E_u ″(² T _2u ) (16 800 cm^-1), and E_g ″(² T _2g )→ U_u ′(² T _2u ) (～ 18 300 cm^-1). Both our absorption and M.C.D. data strongly suggest a Jahn-Teller splitting of the U_u ′(² T _1u ) state but contradict a previous suggestion of such a splitting of the U_u ′(² T _2u ) state. Consideration of σ—π mixing in the t _1u (π + σ) molecular orbital suggests that the ～17 300 cm^-1 band arises from the orbitally-forbidden E_g ″(² T _2g )→ E_u ′(² T _1u ) transition. Bands in the 11 000–13 000 cm^-1 region are assigned to parity-forbidden charge-transfer transitions to states generated by the t _1g (π)→ t _2g excitation. The fine structure seen at liquid helium temperature in K₂SnBr₆ : Ir⁴⁺ both in the 14 500 cm^-1 band and overlying the E_g ″→ U_u ′(² T _2u ) band appears to be associated with parity-forbidden transitions.     

Optical absorption and emission from irradiated RbMgF3:Eu2+ and KMgF3:Eu2+

The optical properties of irradiated RbMgF₃:Eu²⁺ and KMgF₃:Eu²⁺ have been investigated. Previous research has shown that Eu²⁺ ions in unirradiated RbMgF₃ give rise to broad band absorption around 250 nm and sharp intense line emission at 360 nm. When this material is irradiated little or no change occurs in the 250 nm absorption, but the lifetime of the Eu²⁺ 360 nm transition is reduced. In addition, new emission is observed at 680 nm. In the case of irradiated KMgF₃:Eu²⁺ two new emission bands are observed at 600 and 800 nm. All of these transitions have short lifetimes and are not due to Eu³⁺ ions.     

Magnetic circularly polarized emission and magnetic circular dichroism of resolved vibronic lines in Cs2GeF6: Mn4+

Magnetic circularly polarized emission (M.C.P.E.) and magnetic circular dichroism (M.C.D.) techniques have been used to study at low temperatures resolved vibronic lines of the ⁴ A _2g ?² E_g transition in octahedral Mn⁴⁺(3d³) in the cubic host Cs₂GeF₆. Measurements have been made with applied magnetic field (and light propagation) along the [001] (F-Mn-F bond) and [111] directions. Though the Zeeman energy patterns are isotropic, the intensity patterns are not, and U′(Γ₈) eigenvectors for arbitrary field orientation have been derived. These have been used to calculate Zeeman intensity patterns for the [001] and [111] crystallographic directions, and the observed intensity variations with orientation are found to provide useful information about intensity mechanisms. In the case of the magnetic dipole origin, the intensity patterns as a function of orientation can be well accounted for by a first-order mechanism which, however, does not predict the small positive M.C.D. observed at the zero-field energy in the [111] orientation. A detailed analysis of this feature and previously measured energy spacings suggest that ζ_3d(Mn⁴⁺) should have a value of ～360 cm^-1 rather than the value 240 cm^-1 usually assumed. Electric dipole vibronic sidebands have been observed corresponding to v ₆(t _2u ), v ₄(t _1u ), v ₃(t _1u ), v ₄(t _1u ) + v ₅(t _2g ) and v ₂(e_g ) + v ₆(t _2u ). Using a U′→U′ vibronic intensity mechanism with spin-orbit mixing (Appendix A), the M.C.P.E. and total emission patterns for the first two of these regions can be quite well accounted for quantitatively. The corresponding M.C.D. in both cases, while in qualitative agreement with the M.C.P.E., shows much more complicated splitting patterns which are not explicable in terms of a simple k = 0 model. The other three vibronic regions can be accounted for qualitatively. In Appendix B a formula is derived which explicitly relates the M.C.P.E. of a vibronic emission line to its M.C.D. absorption counterpart.     

Magnetic circular dichroism and absorption spectra of Cs2ZrCl6:Mo4+

Absorption and magnetic circular dichroism (M.C.D.) spectra of Mo⁴⁺ in Cs₂ZrCl₆ have been recorded under high resolution at liquid helium temperature over the range 20 000–38 000 cm^-1. All of the bands can be assigned to parity-allowed, ligand-to-metal charge-transfer transitions in both MoCl₆ ^2-(4d²) and an impurity ion which has been identified as MoOCl₅ ^2-(4d¹). The d¹ and d² systems are easily distinguished by the temperature dependence of their M.C.D. spectra, and detailed assignments are proposed for the latter. The absorption spectrum in the region 23 000–26 000 cm^-1 has recently been attributed to a d→d transition in the ion MoCl₆ ^-(4d¹) [1], but the M.C.D. spectrum proves this assignment to be incorrect, and we find no evidence for the presence of this singly-charged species. From the temperature dependence of the M.C.D. spectrum of MoCl₆ ^2-, we estimate the second-order spin-orbit splitting of the E and T ₂ components of the ³ T _1g ground state to be 27 ± 5 cm^-1 with E lowest. The electrostatic splitting of the ³ T _2u and ⁵ T _2u charge-transfer states arising from the t _1u (π + σ) →t _2g excitation is estimated to be close to 515 cm^-1.     

Absorption and magnetic circular dichroism spectra of Cs2ZrBr6: Os4+

High resolution absorption and magnetic circular dichroism (M.C.D.) spectra for Cs₂ZrBr₆ : Os⁴⁺ are reported at liquid helium temperature over the range 17 000–31 000 cm^-1. These results in conjunction with previous work on Cs₂ZrCl₆ : Os⁴⁺ provide a study of the Os⁴⁺ spectrum as a function of ligand spin-orbit coupling constant. The present results strongly support the previous ligand-to-metal charge-transfer interpretation formulated in the j-j limit, described by Piepho et al. [6]. The strong absorption bands can be assigned with confidence to specific, allowed charge-transfer transitions, and detailed assignments are suggested for the less intense features on the basis of forbidden (vibrationally-induced) charge-transfer transitions. Aside from the low energy region (? 16 000 cm^-1) not reported in this work, there seems to be no reason for assigning any important spectral features to d →d transitions.     

The magnetic circular dichroism spectra of matrix-isolated benzene

The magnetic circular dichroism (MCD) spectra of the ¹ B _2u ←¹ A _1g transition of benzene in nitrogen and argon matrices at 20 K have been measured in order to obtain a spectrum devoid of hot bands and complicating rotational structure. The spectrum is dominated by three progressions of B terms, two of positive sign and one of negative. One positive progression and the negative one can be definitely assigned to the e_2g modes v ₆ and v ₉ respectively, whilst the other positive progression may be the e _2g mode v ₈. This is in marked contrast with the absorption spectra of the same matrices which reveal only a single progression built upon v ₆. The MCD spectra are nicely accounted for in terms of a magnetic mixing between the ¹ B _1u and ¹ B _2u states, the electric dipole intensity arising from the mixing in of a ¹ E _1u state via e _2g vibrational modes.     

α—NiSO4.6H2O晶体磁园二色谱和吸收谱的研究

用磁园二色谱和光吸收谱对α－ＮｉＳＯ４．６Ｈ２Ｏ晶体进行了测量和研究，实验结果表明在λ＝１８５～３３００ｎｍ范围内存在一系列吸收结构，其中三个主要主要吸收带结构分别对应于晶体中Ｎｉ离子基态到有关激发态的ｄ－ｄ跃迁，对它们进行了初步指认，实验中观测到红带的λ＝６５４ｎｍ和λ＝７１３ｎｍ两结构间存在一系列弱的结构峰，它们主要与自旋轨道耦合相互作用结果有关，在磁园二色谱中还观测到λ＝５８５ｎｍ的强吸收峰     

Role of magnetic circular dichroism in all-optical magnetic recording

Using magneto-optical microscopy in combination with ellipsometry measurements, we show that all-optical switching with polarized femtosecond laser pulses in ferrimagnetic GdFeCo is subjected to a threshold fluence absorbed in the magnetic layer, independent of either the excitation wavelength or the polarization of the laser pulse. Furthermore, we present a quantitative explanation of the intensity window in which all-optical helicity-dependent switching (AO-HDS) occurs, based on magnetic circular dichroism. This explanation is consistent with all the experimental findings on AO-HDS so far, varying from single- to multiple-shot experiments. The presented results give a solid understanding of the origin of AO-HDS, and give novel insights into the physics of ultrafast, laser controlled magnetism.     

Negative magnetic circular polarization of the A-band emission in KI:Sn2+

Magnetic circular polarization of the emission produced by A-band excitation in KI:Sn²⁺ has been obtained. At low temperatures, when the field is applied along 〈001〉, the emission shows a net negative circular polarization; however, when the field is along 〈111〉, the emission shows the usual positive circular polarization. The unexpected negative polarization can be explained qualitatively by the effect of a charge-compensating vacancy located in the nearest neighbor position.     

Spin-polarization and x-ray magnetic circular dichroism in GaAs

The combination of angular spin momentum with electronics is a promising successor to charge-based electronics. The conduction bands in GaAs may become spin-polarized via optical spin pumping, doping with magnetic ions, or induction of a moment with an external magnetic field. We investigated the spin populations in GaAs with x-ray magnetic circular dichroism for each of these three cases. We find strong anti-symmetric lineshapes at the Ga L₃ edge indicating conduction band spin splitting, with differences in line width and amplitude depending on the source of spin polarization.     

Spin state transition in LaCoO3 studied using soft x-ray absorption spectroscopy and magnetic circular dichroism

Using soft x-ray absorption spectroscopy and magnetic circular dichroism at the Co-L(2,3) edge, we reveal that the spin state transition in LaCoO3 can be well described by a low-spin ground state and a triply degenerate high-spin first excited state. From the temperature dependence of the spectral line shapes, we find that LaCoO3 at finite temperatures is an inhomogeneous mixed-spin state system. It is crucial that the magnetic circular dichroism signal in the paramagnetic state carries a large orbital momentum. This directly shows that the currently accepted low- or intermediate-spin picture is at variance. Parameters derived from these spectroscopies fully explain existing magnetic susceptibility, electron spin resonance, and inelastic neutron data.     

Magnetic circular and linear dichroism in cubic high spin d5 complex

Magneto-optical parameters useful for the interpretation of magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) spectra of high spin d⁵ complexes in tetrahedral or octahedral crystalline fields have been calculated. Two possible intensity borrowing mechanisms—one involving spin-orbit (s.o.) interaction of the ground sextet with the excited quartet states and the other involving the s.o. interaction of an excited charge transfer sextet with the excited quartet states—have been considered for electric dipole transitions in T_d symmetry and for magnetic dipole transitions in O_h symmetry. Of the numerous other mechanisms which may induce electric dipole oscillator strength in O_h symmetry complexes, eight (those in involving odd parity T _1u or T _2u states vibronically induced via t _1u or t _2u vibrational modes) have been investigated in detail. In each of these mechanisms, parameters have been calculated for transitions to all individual s.o. components of all excited quartet states. It is shown how the MCD and MLD techniques, if used in combination, may provide specific information on the mechanism of intensity borrowing and on the spectroscopic assignments of individual s.o. components.     

High resolution absorption and magnetic circular dichroism of spin-forbidden ligand field transitions in Cs3CoBr5

The axial absorption spectrum of Cs₃CoBr₅ has been recorded from 3100 to 6500 Å at 4·2 K with a spectral bandpass of 0·1 Å and the magnetic circular dichroism spectrum at 4·2 K and 47·5 kG over the same wavelength range with a spectral bandpass of 1 Å. The electronic origins of the spinorbit and tetragonal field components of most of the doublet ligand field states are definitively located and assigned. In a number of instances it has also proved possible to determine whether the doublet gains its intensity from the 3/2 U′ or 5/2 U′ spin-orbit component of ⁴ T ₁, and arguments are also presented to show that the higher energy doublets derive the greater part of their intensity from the lowest ⁴ T ₁ charge transfer state and not the ⁴ T ₁(P) ligand field state. The vibronic sidebands accompanying the doublet transitions are also assigned to internal modes of CoBr₄ ^2- and to lattice modes. In a number of the transitions non-totally symmetric modes are excited with greater intensity than totally symmetric.