Magnetic Circular Dichroism Spectra Research Articles

Pure Spin Transport in YIG Films with Amorphous‐to‐Crystalline Transformation

AbstractMagnetic insulators, especially Y3Fe5O12 (YIG), are considered promising candidates for spin‐based device applications due to their ultralow damping, high spin injection efficiency, and long‐distance spin propagation. However, these intriguing features are widely studied based on crystallization YIG films. Pure spin phenomena, like spin transport in YIG films with structural evolution, remain unclear. Herein, pure spin transportation is systematically investigated in the sandwich structure formed by YIG, the inserted layer‐nominal YIG (n‐YIG) with a varied crystalline structure and heavy metal Platinum (Pt). By applying ferromagnetic resonance (FMR)‐driven inverse spin Hall effect (ISHE) measurement, the detected ISHE voltage signal presented a strong correlation with the thickness of n‐YIG and its crystalline phase. A significant increasement in spin transportation is obtained for the crystallized n‐YIG via a high‐temperature annealing. These results demonstrate that pure spin current is transported availably in the structural evolution of YIG films. Furthermore, the element‐specific X‐ray absorption spectroscopy (XAS) and X‐ray magnetic circular dichroism (XMCD) spectra on the n‐YIG films showed a distinction for the crystallized n‐YIG which indicates that the spin propagation is correlated to its magnetic order. These findings are instructive for low‐dissipation spin‐based devices.

Nature of magnetic circular dichroism and absorption spectra of f-f transitions in Na0.4Ho0.6F2.2 single crystal

We present first study of magnetic circular dichroism (MCD) spectra of Ho3+ ion in C4v local symmetry, which it has in fluorite Na0.4Ho0.6F2.2. Optical absorption and MCD spectra were studied in this single crystal in the region of 5I8→ 5F3, 5F2, 3K8 and 5G5 transitions in the temperature range 3.6–––90 K. It was revealed, that number of transitions observed in the MCD and absorption spectra coincides with the number of transitions only from the doublet E state to singlet excited states. The E-E type transitions are not active in MCD, but they are not observed in the absorption spectra either. Paramagnetic magneto-optical activities (MOA) of the absorption bands and their temperature dependences were measured and interpreted with the help of the theory based on the nature of f-f transitions allowance. The MCD spectra were also analyzed in approximation of the J,±MJ wave functions of the free atom. It was shown in particular, that the lowest initial state of the transitions observed at T > 10 K had MJ = 7, but this is not the lowest state of the holmium ion in the crystal. A little lower there is a quasi-doublet with MJ = 8 and, accordingly, with a higher magneto-optical activity of transitions from it. However, the intensity of transitions from this state is low.

Czochralski growth, optical and magneto-optical properties of Ce9.33(SiO4)6O2 crystal

Ce9.33(SiO4)6O2 (CSO) crystals were grown by the Czochralski (Cz) method. Rietveld refinement of XRD patterns confirmed the oxyapatite structure of CSO, XPS analysis revealed the valence of Ce ions in CSO crystals. Magnetization curve and temperature dependencies of the magnetic susceptibility were measured, paramagnetic behavior and magnetic anisotropy have been observed. Photoluminescence and Faraday rotation characteristics of the CSO crystal were investigated at room temperature. Verdet constants of CSO were about 1.6 times as large as those of TGG. Baesd on Van Vleck–Hebb theory, the effective transition wavelength and probability of CSO crystal were calculated and compared with other Ce3+-containing crystals. The absorption and magnetic circular dichroism (MCD) spectra of 4f→5d transitions in Ce3+ ions in CSO crystal were studied.

Faraday rotation enhancement for colloidal spherical Au and Ag nanoparticles and their mixtures

So far, magnetooptical (MO) properties of silver nanoparticles (AgNPs) have been studied only by magnetic circular dichroism (MCD) spectroscopy at the surface plasmon resonance (SPR) band. However, direct knowledge of the Faraday rotation effect (FR) is very important in fundamental research and applications. In the present work, we study an enhancement of FR of individual gold nanoparticles (AuNPs) and AgNPs and their mixture of colloidal aqueous suspension. The Au and Ag spherical NPs were synthesized independently as colloids in an aqueous suspension and then such mixtures were studied (AgNPs were also studied as a suspension in hexane). The noble metal NPs were characterized by TEM, UV–Vis, and refraction methods. The enhancement of FR of individual NPs was observed and it is consistent with available MCD results. For the mixtures, observed changes of magnitude of FR is small, and coupling of both SPR is rather weak. The obtained FR spectra associated with SPR band have been successfully converted to MCD spectra using the Kramers-Kronig transformation. Calculated MCD spectra are consisted with that obtained by direct measurements.

Electronic structure analysis of phthalocyanine complexes using magnetic circular dichroism and magnetic circularly polarized luminescence spectroscopy.

In the study of phthalocyanine complexes using magnetic circular dichroism (MCD) spectroscopy, the electronic structure of excited states is generally discussed based on the rigid-shift approximation, in which the band profiles for left-handed circularly polarized (lcp) and right-handed circularly polarized (rcp) light are assumed to be the same. This assumption may not necessarily be valid for cases where there are multiple initial states having different geometries. Magnetic circularly polarized luminescence (MCPL) from phthalocyanine complexes can be regarded as an example of such cases, since the two degenerate emission states are split in a magnetic field and can undergo a structural deformation. Here, we investigated an alternative approach, where the lcp and rcp components are independently determined. This method, which we refer to as the direct-separation approach, allows direct determination of the distribution of the two emission states as well as the orbital angular momentum . Using this approach, and the distribution were determined from MCD and MCPL spectra of a series of phthalocyanine complexes. Comparison of the two methods shows that the rigid-shift and the direct-separation approaches give practically equivalent results for the systems under study, but the latter is advantageous for systems where the former is not applicable.

Measurement of the Induced Magnetic Polarisation of Rotated-Domain Graphene Grown on Co Film with Polarised Neutron Reflectivity.

In this paper, we determine the magnetic moment induced in graphene when grown on a cobalt film using polarised neutron reflectivity (PNR). A magnetic signal in the graphene was detected by X-ray magnetic circular dichroism (XMCD) spectra at the C K-edge. From the XMCD sum rules an estimated magnetic moment of 0.3 μB/C atom, while a more accurate estimation of 0.49 μB/C atom was obtained by carrying out a PNR measurement at 300 K. The results indicate that the higher magnetic moment in Co is counterbalanced by the larger lattice mismatch between the Co-C (1.6%) and the slightly longer bond length, inducing a magnetic moment in graphene that is similar to that reported in Ni/graphene heterostructures.

Photophysical Exploration of Two Isomers of Octaethyltrioxopyrrocorphin.

The introduction of three β-oxosubstituents to octaethylporphyrin by means of an oxidation/rearrangement reaction generates the trioxopyrrocorphin chromophore. Pyrrocorphins (hexahydroporphyrins) are generally nonaromatic, but we recently demonstrated trioxopyrrocorphins to possess considerable aromatic character. This contribution explores the photophysical characteristics of these unusual chromophores. In agreement with density functional theory modeling, the UV-vis and magnetic circular dichroism spectra of the two─out of the four possible─triketone regioisomers investigated conform to the Gouterman model of porphyrinoid optical spectra, in alignment with their aromaticity. Their excited-state dynamics shed further light on the degree to which β-oxo substitutions tune the photophysical properties of porphyrinoids. Introduction of β-oxo functionalities increases the rate and yield of intersystem crossing and shortens the triplet state lifetime. Unexpectedly, the singlet oxygen generation yield of both pyrrocorphins remains relatively high, with modes of distortion from planarity likely enhancing triplet energy transfer. This work thus expands our understanding of a rare class of porphyrinoids and further characterizes them as sustaining aromatic porphyrinic π-systems. Our findings suggest triple β-oxo substitution as a viable route toward the development of novel, high-singlet oxygen yield porphyrinic photosensitizers.

Efficient Protocol for Computing MCD Spectra in a Broad Frequency Range Combining Resonant and Damped CC2 Quadratic Response Theory.

Coupled cluster response theory offers a path to high-accuracy calculations of spectroscopic properties, such as magnetic circular dichroism (MCD). However, divergence or slow convergence issues are often encountered for electronic transitions in high-energy regions with a high density of states. This is here addressed for MCD by an implementation of damped quadratic response theory for resolution-of-identity coupled cluster singles-and-approximate-doubles (RI-CC2), along with an implementation of the MCD term from resonant response theory. Combined, damped and resonant response theory calculations provide an efficient strategy to obtain MCD spectra over a broad frequency range and for systems that include highly symmetric molecules with degenerate excited states. The protocol is illustrated by application to zinc tetrabenzoporphyrin in the energy region of 2-8 eV and comparison to experimental data. Timings are reported for the resonant and damped approaches, showing that a greater part of the calculation time is consumed by the construction of the building blocks for the final MCD ellipticity. A recommendation on how to use the procedure is outlined.

DIBENZOCYCLOOCTADIENE LIGNANS ISOLATED FROM THE ROOTS OF SCHISANDRA CAULIFLORA AND THEIR NITRIC OXIDE INHIBITION ACTIVITY ON LPS STIMULATED RAW 264.7 CELLS

Objectives: To isolate and determine the chemical structure of some compounds from the roots of Schisandra Cauliflora and their inhibitory activity on nitric oxide production. Methods: The roots of Schisandra cauliflora, which were collected in Vinh Phuc in April 2022, were processed before being extracted and isolated to obtain compounds. Compounds structures were elucidated based on extensive spectroscopic analyses, including 1D- and 2D-nuclear magnetic resonance spectroscopy (NMR), mass spectrometry (HR-ESI-MS), and CD spectra. The obtained compounds were evaluated for inhibitory activity on nitric oxide production on LPS stimulated RAW 264.7 cells. Results and conclusion: From the methanol extract of the roots of Schisandra cauliflora, three dibenzocyclooctadiene lignans were isolated, including ananonin J, ananolignan F, and ananolignan C. Their structures were elucidated. All the compounds inhibited nitric oxide productions on LPS stimulated RAW 264.7 cells with IC50 values of 45.24 ± 1.46, 41.32 ± 1.45, and 48.71 ± 1.34µM, respectively, compared to that of the positive control of dexamethasone (IC50 14.20 ± 0.54µM). This is the first time these lignan compounds have been isolated from the roots of Schisandra cauliflora.

Variable spin texture in Mn3Sn/Pt heterostructures revealed by magnetic circular dichroism

Non-collinear antiferromagnets with a D019 hexagonal structure have attracted tremendous attention for their potential applications in topological spintronics. Exploring the relationship between spin texture and electronic band structure is crucial for understanding the physical nature of these chiral antiferromagnets. Here, we systematically investigated the variation of topological spin texture of the non-collinear antiferromagnet Mn3Sn film using magnetic circular dichroism (MCD) spectroscopy. The evolution of Mn spin texture from coplanar inverted triangular structure to swirling spin texture was achieved in Mn3Sn/Pt heterostructures through introducing an interfacial Dzyaloshinskii–Moriya interaction (DMI) at room temperature. Correspondingly, unconventional zero-crossing points in energy-resolved MCD spectra as well as a gradual shift of a zero-crossing point to longer wavelength were observed. Our work provides a spin texture modulation approach via interfacial DMI and an effective non-contact magneto-optical detection method to reveal the spin texture in the non-collinear antiferromagnet/heavy metal system.

Magnetic Circular Dichroism of Porphyrinoid Silver Complexes: Evidence of the Electronic Structure Inversion upon Protonation of the N-Confused Core.

We report a systematic investigation of a series of Ag(II) and Ag(III) complexes of porphyrins and their analogues using UV-vis magnetic circular dichroism (MCD) spectroscopies and theoretical calculations. Ag(II) and Ag(III) octaethyl- and tetraarylporphyrins show the usual sign sequence in the Q-band region (i.e., negative to positive intensities with increasing energy) of their MCD spectra, indicative of the ΔHOMO > ΔLUMO relationship (ΔHOMO is the energy difference between Michl's a and s orbitals, and ΔLUMO is the energy difference between Michl's -a and -s pair of MOs). In contrast, Ag(II) complexes of β,β'-pyrrole-modified porphyrins (with an effective chlorin-type π-system) and Ag(III) corroles have sign reverse features in the MCD spectra of their Q-band region (ΔHOMO < ΔLUMO relationships). The Ag(III) complex of N-confused porphyrin shows the ΔHOMO > ΔLUMO relationship in the neutral state and the ΔHOMO < ΔLUMO relationship in the protonated form.

Plasmon-exciton coupling in Au nanosphere/carbocyanine J-aggregate hybrids assessed by magnetic circular dichroism (MCD) spectroscopy

In this study, we evaluate plasmon-exciton coupling in Au nanosphere/carbocyanine J-aggregate hybrids by magnetic circular dichroism (MCD) spectroscopy. The carbocyanine dye we used is JC-1, which adsorbs onto Au nanospheres to form J-aggregates. The hybrids exhibit a double-peaked extinction spectrum, and a shallow dip appears at the resonance position of the native J-aggregates, indicating the presence of plasmon-exciton interactions. MCD spectra of the hybrids show a derivative-like profile originated from the surface plasmon resonance of Au nanospheres accompanied by an additional distinct dip (or bump) caused by the exciton resonance of the adsorbed J-aggregates. Importantly, the MCD dip (or bump) position does not correspond to that of the observed new extinction peak, but agrees well with the extinction dip. Moreover, we find that the linewidths of the MCD dip (or bump) are narrow and comparable to that of the J-band of the dye aggregates. All the results suggest that the present hybrid systems are categorized in a weak-coupling regime. Hence we believe that MCD will be a useful spectroscopic method to effectively assess the plasmon-exciton interactions in various kinds of plasmonic-excitonic nanohybrid systems.

Magnetic properties of Cr-doped VO2 thin films in tetragonal phase of rutile and their synchrotron-based electronic structures

The present study is focused on the investigation at 400 K of the tetragonal-rutile phase of Cr-doped VO2 (CVO) thin films grown by pulsed laser deposition. Synchrotron-based x-ray measurements of both the surface-sensitive total electron yield (TEY) and bulk-sensitive total fluorescence yield (TFY) modes were used to investigate the pristine and Cr-doped VO2 (5%, 10%, 20%, and 30% of atomic weight). The structural analysis and purity of the crystalline phase of the as-deposited films are manifested via grazing incidence x-ray diffraction patterns, which confirm the tetragonal-rutile phase. The purity of the phase is also confirmed by the presence of Eg-mode phonons in the Raman spectra and its deconvolution reflects on the oxygen-mediated electronic/vibrational transitional effect. A clear hysteretic behavior obtained through vibrating sample magnetometry strongly suggests the ferromagnetic interaction in the thin films of CVO. The local-electronic property of the samples is examined using x-ray absorption spectroscopy (XAS) in TEY and TFY modes where the difference in the configured helicity photons resulted in the fine spectra of x-ray magnetic circular dichroism (XMCD). XAS and XMCD measurements performed at V L2,3 and Cr L2,3 edges explicitly demonstrate the ferromagnetism in the thin films of CVO. The strong hybridization between V 3d and Cr 3d states with O 2p states is evident from the spectra of the O K-edge, resulting in the onset of the cation-pair formation V5+–Cr3+, which is ferromagnetic by means of double-exchange interaction. The theoretical calculation of density functional theory made upon Vienna ab initio simulation package suggests that CVO is in a mixed state of a ferromagnetic-insulator and a half-metallic ferromagnet.

Anisotropic hybridization probed by polarization dependent x-ray absorption spectroscopy in VI3 van der Waals Mott ferromagnet

Polarization dependent x-ray absorption spectroscopy was used to study the magnetic ground state and the orbital occupation in bulk-phase VI3 van der Waals crystals below and above the ferromagnetic and structural transitions. X-ray natural linear dichroism and x-ray magnetic circular dichroism spectra acquired at the V edges are compared against multiplet cluster calculations within the frame of the ligand field theory to quantify the intra-atomic electronic interactions at play and evaluate the effects of symmetry reduction occurring in a trigonally distorted VI6 unit. We observed a non zero linear dichroism proving the presence of an anisotropic charge density distribution around the V3+ ion due to the unbalanced hybridization between the vanadium and the ligand states. Such hybridization acts as an effective trigonal crystal field, slightly lifting the degeneracy of the ground state. However, the energy splitting associated to the distortion underestimates the experimental band gap, suggesting that the insulating ground state is stabilized by Mott correlation effects rather than via a Jahn–Teller mechanism. Our results clarify the role of the distortion in VI3 and establish a benchmark for the study of the spectroscopic properties of other van der Waals halides, including emerging 2D materials with mono and few-layers thickness, whose fundamental properties might be altered by reduced dimensions and interface proximity.

Role of MCD and Mössbauer Spectroscopy in the Explanation of the Properties of a Highly Soluble (μ-Oxo)bis[tetra(tert-butyl)(phthalocyaninato)iron(III)] Complex, Its Pyridine Adduct, and Redox Forms Oxidized under Anaerobic Conditions in Non-Coordinating Solvents.

Solid-state Mössbauer spectra of a highly soluble (μ-oxo)bis[tetra(tert-butyl)(phthalocyaninato)iron(III)] complex 1 ((PctBuFe)2O) consist of two doublets that represent bent geometry in μ-oxo(1) (1a, ΔEQ = 0.43 mm/s, T = 10 K) and linear geometry in μ-oxo(2) (1b, ΔEQ = 1.40 mm/s, T = 10 K) isomers with the ratio between two isomers depending on the purification method. Both isomers were found to be diamagnetic and transform entirely to the 1a isomer in solution. The room- and low-temperature magnetic circular dichroism (MCD) spectra of 1a μ-oxo(1) show one Faraday A- and one B-term between 670 and 720 nm, which correlate with the 690 nm band and 709 nm shoulder observed in the UV-vis spectrum of this compound. UV-vis and MCD spectra of 1a are almost independent of the temperature. Both 1a and 1b are diamagnetic between room temperature and 4 K. Electrochemical experiments show up to three oxidations and up to four reduction processes in 1a. Its oxidation under spectroelectrochemical or chemical (in the absence of oxygen-containing oxidants) conditions in non-coordinating solvents results in the formation of broad NIR bands around 1195 nm (first oxidation) and 1264 nm (second oxidation). The MCD spectra of the redox-active species show a Faraday B-term signal with negative amplitude in this region and are very different from those in the monomeric PctBu(1-)FeIIIX2 complexes 5X (X = Cl- or CF3CO2-). The pyridine adduct of 1a ((PyPctBuFe)2O; 2Py) is paramagnetic (μB = 2.19, g = 2.11, and J = -6.1 cm-1) and has a major peak at 627 nm of its UV-vis spectrum, which is associated with a MCD pseudo A-term. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, along with the exciton coupling theory, were used to explain the unusually red-shifted intense transitions in 1a as well as the H-aggregate-like spectra of the pyridine adduct 2Py.

Optical transitions in nonstoichiometric cerium oxide (CeO2–x) nanoparticles resolved by magnetic circular dichroism (MCD) spectroscopy

We for the first time present magnetic circular dichroism (MCD) spectra in nonstoichiometric CeO2–x nanoparticles with different sizes and morphologies. A derivative-like MCD profile is found at around the absorption maximum, but the MCD zero-crossing position does not always agree with the absorption peak. Such behaviors can reasonably be accounted for two interacting Faraday B-terms (or transitions) that are associated with the spin–orbit coupling of Ce4+-based transitions from O 2p to Ce 4f states. Additionally, on the basis of both absorption and MCD spectral analysis, we proposed a new method to approximately estimate the Ce3+/Ce4+ ratio.

Exciton Linewidth and Exciton‐Phonon Coupling in 2H and 3R Bilayer WS2 Studied by Magnetic Circular Dichroism Spectrum

AbstractLayered transition metal dichalcogenides (TMDs) are a promising platform for new photonic and optoelectronic devices. Exciton‐phonon interaction is critical in determining their characteristics such as the exciton coherence lifetime and linewidth. However, the exciton linewidth obtained by conventional reflection spectrum is greatly affected by the background signals, and the research into exciton‐phonon coupling difference induced by stacking‐order in multi‐layer structures is still lacking. In this work, the temperature‐dependent exciton linewidths of CVD‐grown large‐area monolayer, 2H and 3R‐stacking bilayer WS2 based on a self‐designed reflective magnetic circular dichroism (MCD) spectrum are systematically investigated. It is found that 2H‐bilayer WS2 exhibits significantly larger exciton linewidth compared with monolayer and 3R bilayer, which can be attributed to the appearance of new phonon‐assisted relaxation channels caused by interlayer coupling. Meanwhile, 3R bilayer with a redshifted exciton peak has a narrower linewidth than 2H phase because the interlayer hopping is suppressed, resulting in the absence of interlayer scattering channel. These results provide intuitive evidence for the exciton linewidth‐broadening and exciton‐phonon coupling in different stacked layers and open up new vistas for the development of TMD‐based narrow‐linewidth nano‐sensors devices.

Spin–Charge Conversion in Hybrid Structure PbZrO3/Y3Fe5O12/Pt

Multifunctional oxide heterostructures exhibiting magnetoelectric properties show great potential in advanced applications which are attracting a number of recent investigations. Herein, hybrid structures are presented including the antiferroelectricity film PbZrO3 (PZO) and the ferrimagnetic insulator (FMI) yttrium iron garnet (Y3Fe5O12, (YIG)) film by means of pulse laser deposition and magnetron sputtering, respectively. A visible double ferroelectricity hysteresis loop for PZO at low electrical field and the distinct X‐ray magnetic circular dichroism (XMCD) spectra for YIG are obtained. To study the spin current transfer processes between platinum (Pt) and the PZO/YIG system, the Pt film is deposited on the PZO/YIG bilayers as the conversion detector and the spin–charge conversion voltage can be obtained via inverse spin Hall effect (ISHE) under thermal gradient excitation. These results indicate that the hybrid structure PZO/YIG/Pt provides a potential route to realize an electric field control of spin–charge conversion and is instructive for future low‐power multiferroic heterostructures‐based spintronic devices.

Synthesis of Peripherally Annulated Phenanthroporphyrins.

Synthesis of unusual phenanthroporphyrins was achieved by a stepwise precursor method. Precursor porphyrins fused with aryl-substituted bicyclo[2.2.2]octadiene afforded the corresponding arylbenzoporphyrins (arylBPs) by a retro Diels-Alder reaction. Unusual phenanthroporphyrins were obtained via the intramolecular Scholl reaction of arylBPs. X-ray crystallographic analysis revealed a distorted, helical porphyrin plane. Red-shifted absorptions of tetraphenanthroporphyrin are observed at ca. 580 nm for the B band and at 700-900 nm for the Q bands. Analysis of magnetic circular dichroism spectra and time-dependent density functional theory calculations was used to explain the optical properties and electronic structures.

Including vibrational effects in magnetic circular dichroism spectrum calculations in the framework of excited state dynamics.

In this work, we present a computational approach that is able to incorporate vibrational effects in the computations of magnetic circular dichroism (MCD) spectra. The method combines our previous implementations to model absorption as well as fluorescence and phosphorescence spectra in the framework of excited state dynamics with a new technique to calculate MCD intensities, where molecular orientational averages are treated via semi-numerical quadrature. The implementation relies on a path integral approach that is employed to compute nuclear dynamics under the harmonic oscillator approximation (accounting for the nuclear potential energy surface) together with quasi-degenerate perturbative theory (to include the perturbation of an external magnetic field). We evaluate our implementation with a selected molecular set consisting of five aromatic organic molecules, namely, 1,4-benzoquinone, naphthalene, 2-naphthylamine, 2-naphthaldehyde, and benzene; we also included the MnO4- and the [Co(NH3)6]3+ transition metal complexes. This set is used to validate the ability of the approach to compute MCD A- and B-terms in conjunction with time-dependent density functional theory. The computed intensities are discussed in terms of the overall quality of the electronic structure treatments, vibrational modes, and the quality of the nuclear Hessians. It is shown that in the cases in which the potential energy surface is accurately represented, electric dipole-forbidden transitions are vibrationally activated, producing intensities relative to the dipole-allowed transitions in the same order of magnitude as the experimental measurements.