Magnetic Circular Dichroism Research Articles

Electrospinning of Self-Assembling Oligopeptides into Nanofiber Mats: The Impact of Peptide Composition and End Groups.

Low-molecular-weight oligopeptides can be electrospun into nanofiber mats. However, the mechanism underlying their electrospinnability is not well-understood. In this study, we used solid-phase peptide synthesis to produce the oligopeptide FFKK, to which the aromatic end-capping groups naphthalene, pyrene, and tetraphenylporphyrin were attached. Nuclear magnetic resonance, circular dichroism, and electrospray ionization mass spectrometry were used to characterize the oligopeptide structures. We investigated the effect of end-caps and oligopeptide concentration on their self-assembly as well as on their electrospinnability in fluorinated solvents. All oligopeptides with aromatic end-caps were amenable to electrospinning. Attenuated total reflectance Fourier transform infrared spectroscopy and microrheology results support the hypothesis that at sufficiently high concentrations, the self-assembled structures interact strongly, which facilitates electrospinning. Moreover, the results from this fundamental study can be extended to nonpeptidic small molecules possessing strong intermolecular interactions.

Tailoring of Creep Regime Domain Wall Dynamics in Perpendicularly Magnetized Pd/Co/Pd Trilayers

AbstractUnderstanding magnetic domain wall (DW) dynamics is vital for improving the performance of heavy metal/ferromagnet based spintronic devices. Pd/Co/Pd multilayers hosting perpendicular magnetic anisotropy and interfacial Dzyaloshinskii‐Moriya interaction are prototypes for high density magnetic memory devices. This work presents the creep regime DW dynamics in Pd/Co/Pd trilayers with Ta buffer layer excited by symmetric field‐induced domain wall motion using Kerr microscopy. A systematic increment of DW velocity with increasing Co thickness is observed. SQUID‐VSM measurements reveal that the effective anisotropy constant decreases with the Co layer, leading to an increased DW width. Kerr microscopy images confirm that the DW is becoming rougher with magnetic layer thickness because of the dominance of magnetostatic energy over the DW energy. Hard X‐ray photoemission spectroscopy (HAXPES) reveals the presence of alloying at interfaces of Co/Pd. The asymmetry in magnetic circular dichroism HAXPES at the Pd 3d edge pictures the induced magnetic moment in Pd which is consistent with the larger saturation magnetization obtained from vibrating sample magnetometry. Extended X‐ray absorption fine structure performed in out‐of‐plane and in‐plane geometry shows the disordered nature of the Co local environment with the interdiffusion of Pd atoms into Co causing an asymmetry in the bonds.

Theoretical and Spectroscopic Analysis of Square-Planar Tellurium(II) and Selenium(II) Diphenyl Thiourea Complexes in p2 Electronic Configurations.

In this work, we performed a detailed mathematical ligand field theory analysis of square-planar (D4h) main group complexes in p2 electronic configurations, and the results were subsequently used to generate an energy-level correlation diagram. We synthesized the model p2 tellurium(II) diphenyl thiourea coordination complex for further spectroscopic investigation. Dissolution of TeO2 in concentrated HCl resulted in the formation of a [TeCl6]2- complex in acidic media, and subsequent addition of diphenyl thiourea resulted in the reduction of Te4+ to Te2+ (observed by 125Te NMR spectroscopy) and the formation of a cis-Te(dptu)2Cl2 complex, which was characterized by single-crystal X-ray diffraction (XRD). Using in situ optical/magnetic spectroscopy - specifically, UV-vis and magnetic circular dichroism (MCD) spectroscopy - we observed absorbance bands and polarized transitions consistent with the calculated p-orbital splitting in a square planar (D4h) ligand field. Using the results of our spectroscopic investigation, we generated a molecular orbital (M.O.) diagram for the cis-Te(dptu)2Cl2 complex. We then used the M.O. diagram, in conjunction with the energy level correlation diagram, to assign the electronic transitions observed in the spectra of the cis-Te(dptu)2Cl2 complex. The analogous selenium(II) complex, cis-Se(dptu)2Cl2, was used to elucidate the observed transitions with minimal contribution from spin-orbit coupling. Our work examined how in situ spectroscopy and complementary ligand field theory analysis can be used to elucidate the electronic structures of main group coordination complexes.

Natural and Magnetic Circular Dichroism from the Infrared to the UV of a Hetero[4]Helicene Radical Cation.

Dithiabridged triarylamine hetero[4]helicenes are an interesting class of chiral compounds characterized by a high racemization barrier which makes them an attractive material for several applications. Their rich redox chemistry allows one to obtain radical cations stable at room temperature, that can be isolated in two configurationally stable enantiomers. While several studies have been reportedon systems with transition metals possessing low-lying electronic states, the characterization of purely organic openshell systems by VCD is still scarce. This may be due to the instability of radical-cation species and to the dark color assumed by the solution at the high concentration required by VCD. The oxidation of this molecular system shifts the first electronic transition towards the Near-IR (NIR) region, at approximately 1250 nm. By combining ECD, VCD, MCD, NIR-CD and computational methodologies rooted in density functional theory, we have investigated one molecule of this class of compounds and shed some light on the chiroptical properties accessible via redox-switch.

Voltage-Gated 90° Switching of Bulk Perpendicular Magnetic Anisotropy in Ferrimagnets.

Unraveling the mechanism behind bulk perpendicular magnetic anisotropy (PMA) in amorphous rare earth-transition metal films has proven challenging. This is largely due to the inherent complexity of the amorphous structure and the entangled potential origins arising from microstructure and atomic structure factors. Here, we present an approach wherein the magneto-electric effect is harnessed to induce 90° switching of bulk PMA in Tb-Co films to in-plane directions by applying voltages of only -1.2 V. This manipulation is achieved by voltage-driven insertion of hydrogen atoms into interstitial sites between Tb and Co atoms, which serves as a perturbation to the local atomic structure. Using angle-dependent X-ray magnetic circular dichroism, we find that the anisotropy switching originates from the distortion of the crystal field around Tb, which reorients the alignment of Tb orbital moments. Initially aligned along Tb-Co bonding directions, the easy magnetization axis undergoes reorientation and switches by 90°, as substantiated by ab initio calculations. Our study not only concludes the atomic origin of Tb-Co atom bonding configuration in shaping bulk PMA but also establishes the groundwork for electrically programmable ferrimagnetic spintronics, such as controlling domain wall motion and programming artificial spin textures.

ULtimate MAGnetic characterization (ULMAG) at the ID12 beamline of ESRF: from element-specific properties to macroscopic functionalities

We present a novel instrument designed for advanced magnetic study, installed at the ID12 beamline of the European Synchrotron Radiation Facility in Grenoble, France. This instrument offers the unique capability to simultaneously measure element-specific microscopic and macroscopic properties related to the magnetic, electronic and structural characteristics of materials. In addition to X-ray absorption, X-ray magnetic circular dichroism alongside X-ray diffraction patterns, the macroscopic magnetization, volume changes, caloric properties and electrical resistivity of magnetic materials could be measured strictly under the same experimental conditions as a function of both magnetic field (up to ±7 T) and temperature (ranging from 2.05 K to 325 K). To demonstrate the capability of this new instrument, we present two case studies highlighting its performance in investigating first-order magneto-structural phase transitions, namely in DyCo2 and FeRh alloys.

Demagnetization Process of Nd‐Fe‐B Sintered and Ferrite Magnets

The magnetization reversal mechanism for Nd‐Fe‐B sintered and ferrite magnets was investigated using magnetic measurements and soft X‐ray magnetic circular dichroism microscopy. In magnetization reversal, discrete reversals of crystal grains occurred first in the demagnetized field region, which was lower than the coercivity. In the next step, clusters of reversed grains were formed by reversals in crystal grains around the discrete reversed grains. For highly aligned magnets, the cluster sizes at the coercivity increased with decreasing temperature, and also varied with composition. The alignment and angular dependences of the coercivity varied with cluster size, which depended on the number of discrete magnetization reversal grains that occurred in the demagnetizing field that was lower than the coercivity. Hence, if the number of discrete reversal grains was large, the cluster size was small; conversely, if the number of discrete reversal grains was small, the cluster size was significant. © 2025 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Proximity-induced flipped spin state in synthetic ferrimagnetic Pt/Co/Gd heterolayers

To develop new devices based on synthetic ferrimagnetic heterostructures, understanding the material’s physical properties is pivotal. Here, the induced magnetic moment (IMM), magnetic exchange coupling, and spin textures are investigated in Pt(1 nm)/Co(1.5 nm)/Gd(1 nm) multilayers using a multiscale approach. The magnitude and direction of the IMM are interpreted in the framework of both X-ray magnetic circular dichroism and density functional theory. The IMM transferred by Co across the Gd paramagnetic thickness leads to a nontrivial flipped spin state (FSS) within the Gd layers, in which their magnetic moments couple antiparallel/parallel with the ferromagnetic Co near/far from the Co/Gd interface, respectively. The FSS depends on the magnetic field, which, on average, reduces the Gd magnetic moment as the field increases. For the Pt, in both Pt/Co and Gd/Pt interfaces, the IMM follows the same direction as the Co magnetic moment, with negligible IMM in the Gd/Pt interface. Additionally, zero-field spin spirals were imaged using scanning transmission X-ray microscopy, whereas micromagnetic simulations were employed to unfold the interactions, stabilizing the ferrimagnetic configurations, where the existence of a sizable Dzyaloshinskii-Moriya interaction is demonstrated to be crucial.

High-Coercivity Ferrimagnet Co₂FeO₂BO₃: XMCD Insights into Charge-Ordering and Cation Distribution

The multi-sublattice ferrimagnet Co2FeO2BO3, a prominent example of lanthanide-free magnets, was the subject of element-selective studies using X-ray magnetic circular dichroism (XMCD) observations at the L- and K- X-ray absorption edges. Research findings indicate that the distinct magnetic characteristics of Co2FeO2BO3, namely its remarkable high coercivity (which surpasses 7 Tesla at low temperatures), originate from an atypical arrangement of magnetic ions in the crystal structure (sp.gr. Pbam). The antiferromagnetic nature of the Co2+-O-Fe3+ exchange interaction was confirmed by identifying the spin and orbital contributions to the total magnetization from Co (mL = 0.27 ± 0.1 μB/ion and meffS = 0.53 ± 0.1 μB/ion) and Fe (mL = 0.05 ± 0.1 μB/ion and meffS = 0.80 ± 0.1 μB/ion) ions through element-selective XMCD analysis. Additionally, the research explicitly revealed that the strong magnetic anisotropy is a result of the significant unquenched orbital magnetic moment of Co, a feature that is also present in the related compound Co3O2BO3. A complex magnetic structure in Co2FeO2BO3, with infinite Co²⁺O6 layers in the bc-plane and strong antiferromagnetic coupling through Fe3⁺ ions, is suggested by element-selective hysteresis data, which revealed that Co²⁺ ions contribute both antiferromagnetic and ferromagnetic components to the total magnetization. The findings underline the suitability of Co2FeO2BO3 for applications in extreme environments, such as low temperatures and high magnetic fields, where its unique magnetic topology and anisotropy can be harnessed for advanced technologies, including materials for space exploration and quantum devices. This XMCD study opens the door to the production of novel high-coercivity, lanthanide-free magnetic materials by showing that targeted substitution at specific crystallographic sites can significantly enhance the magnetic properties of such materials.

Investigation of magnetic properties in Y3Fe5O12/Cr2O3/Pt tri-layers

Abstract Artificial multiferroics combining ferroelectric and magnetic materials exhibits a sizable magnetoelectric coupling and further shows a great potential for realizing low power consumption information processing. In this work, hybrid structures consisting of the ferrimagnetic yttrium iron garnet (Y3Fe5O12, (YIG)) layer and anti-ferromagnetic chromium oxide (Cr2O3) layer are deposited directly onto (110)-oriented single-crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) ferroelectric substrates by means of radio frequency magnetron sputtering and post-annealing procedures. The dynamical properties of YIG films are investigated via ferromagnetic resonance measurements and a low damping constant of 0.00258 is obtained. Combining the element-specific soft x-ray absorption spectroscopy, x-ray magnetic circular dichroism and x-ray magnetic linear dichroism, the magnetic order in YIG film and the Néel order in Cr2O3 layers are further characterized. By capping a platinum (Pt) layer on PMN-PT/YIG/Cr2O3, a visible spin-charge converted signal has been obtained via both spin pumping and spin Seebeck measurements. These results indicate that the artificial multiferroic structures PMN-PT/YIG/Cr2O3/Pt serve as a promising material platform for realizing an efficient manipulation of magnetism via electrical means.

Deposition of plasmonic ITO nanoparticles by near-infrared laser ablation

Compound nanoparticles (NPs) attract attention because of their unique electrical, optical, and catalytic properties. Among them, plasmonic tin-doped indium oxide (ITO) NPs are characterized by transparency in the visible wavelength range and tunable localized surface plasmon resonance (LSPR) in the near-infrared (NIR) range due to high electronic conductivity. To date, they have been usually synthesized by a chemical solution process. However, the chemically synthesized ITO NPs are capped with organic protecting agents, which often block exchange of charge carriers and access of chemical species to the NPs, limiting some applications. In the present study, we propose a method for direct deposition of ITO NPs on a glass or plastic substrate using commercially available ITO-coated glass via NIR laser ablation. The LSPR characteristics of the ITO NPs, thus, prepared were controlled by changing the ablation conditions such as laser power. In addition, the potential applications of the ITO NPs were also investigated through measurements of their refractive index sensitivity and magnetic circular dichroism.

Probing Berry Curvature in Magnetic Topological Insulators through Resonant Infrared Magnetic Circular Dichroism.

Probing the quantum geometry and topology in condensed matter systems has relied heavily on static electronic transport experiments in magnetic fields. Yet, contact-free optical measurements have rarely been explored. Here, we report the observation of resonant magnetic circular dichroism (MCD) in the infrared range in thin film MnBi_{2}Te_{4} exhibiting a spectral intensity that correlates with the anomalous Hall effect. Both phenomena emerge with a field-driven phase transition from an antiferromagnet to a canted ferromagnet. By theoretically relating the MCD to the anomalous Hall effect via Berry curvature for a metallic state, we show that this transition accompanies an abrupt onset of Berry curvature, signaling a topological phase transition from a topological insulator to a doped Chern insulator. Our density functional theory calculation suggests the MCD signal mainly originates from an optical transition at the Brillouin zone edge, hinting at a potential new source of Berry curvature away from the commonly considered Γ point. Our findings demonstrate a novel experimental approach for detecting Berry curvature through spectroscopy of the interband MCD, generally applicable to magnetic materials.

A Spectrochemical Series for Electron Spin Relaxation.

Controlling the rate of electron spin relaxation in paramagnetic molecules is essential for contemporary applications in molecular magnetism and quantum information science. However, the physical mechanisms of spin relaxation remain incompletely understood, and new spectroscopic observables play an important role in evaluating spin dynamics mechanisms and structure-property relationships. Here, we use cryogenic magnetic circular dichroism (MCD) spectroscopy and pulse electron paramagnetic resonance (EPR) in tandem to examine the impact of ligand field (d-d) excited states on spin relaxation rates. We employ a broad scope of square-planar Cu(II) compounds with varying ligand field strength, including CuS4, CuN4, CuN2O2, and CuO4 first coordination spheres. An unexpectedly strong correlation exists between spin relaxation rates and the average d-d excitation energy (R2 = 0.97). The relaxation rate trends as the inverse 11th power of the excited-state energies, whereas simplified theoretical models predict only an inverse second power dependence. These experimental results directly implicate ligand field excited states as playing a critical role in the ground-state spin relaxation mechanism. Furthermore, ligand field strength is revealed to be a particularly powerful design principle for spin dynamics, enabling formation of a spectrochemical series for spin relaxation.

Two-dimensional anion-rich NaCl2 crystal under ambient conditions

The two-dimensional (2D) “sandwich” structure composed of a cation plane located between two anion planes, such as anion-rich CrI3, VS2, VSe2, and MnSe2, possesses exotic magnetic and electronic structural properties and is expected to be a typical base for next-generation microelectronic, magnetic, and spintronic devices. However, only a few 2D anion-rich “sandwich” materials have been experimentally discovered and fabricated, as they are vastly limited by their conventional stoichiometric ratios and structural stability under ambient conditions. Here, we report a 2D anion-rich NaCl2 crystal with sandwiched structure confined within graphene oxide membranes with positive surface potential. This 2D crystal has an unconventional stoichiometry, with Na:Cl ratio of approximately 1:2, resulting in a molybdenite-2H-like structure with cations positioned in the middle and anions in the outer layer. The 2D NaCl2 crystals exhibit room-temperature ferromagnetism with clear hysteresis loops and transition temperature above 320 K. Theoretical calculations and X-ray magnetic circular dichroism (XMCD) spectra reveal the ferromagnetism originating from the spin polarization of electrons in the Cl elements of these crystals. Our research presents a simple and general approach to fabricating advanced 2D unconventional stoichiometric materials that exhibit half-metal and ferromagnetism for applications in electronics, magnetism, and spintronics.

Synthesis of Nanocrystalline Mn-Doped Bi2Te3 Thin Films via Magnetron Sputtering

This study reports the structural and magnetic properties of Mn-doped Bi2Te3 thin films grown by magnetron sputtering. The films exhibit a ferromagnetic response that depends on the Mn doping concentration, as revealed by X-ray magnetic circular dichroism measurements. At an Mn concentration of ∼6.0%, a magnetic moment of (3.48 ± 0.25) μB/Mn was determined. Structural analysis indicated the presence of a secondary MnTex phase, which complicates the interpretation of the magnetic properties. Additionally, the incorporation of Mn ions within the van der Waals gap and substitutional doping on Bi sites contributes to the observed complex magnetic properties. Intriguingly, a decrease in magnetic moment per Mn was observed with increasing Mn concentration, which is consistent with the formation of the intrinsic magnetic topological insulator MnBi2Te4.

Dibohemamines I-O from Streptomyces sp. GZWMJZ-662, an endophytic actinomycete from the medicinal and edible plant Houttuynia cordata Thunb.

A chemical investigation of Streptomyces sp. GZWMJZ-662, an endophytic actinomycete isolated from Houttuynia cordata Thunb., has yielded eleven bohemamine dimers (1-11). Notably, the newly identified dibohemamines I-O (1-7) have not been previously reported. Their structures were elucidated through detailed spectroscopic analysis, encompassing high-resolution electrospray ionization mass, nuclear magnetic resonance, infrared radiation, ultraviolet-visible, and electronic circular dichroism spectroscopy. Dibohemamine I (1) exhibited selective cytotoxic effects against the cancer cell lines 786-O and GBC-SD among the 18 cell lines evaluated, with the half-inhibitory concentration values of 3.24 ± 0.20 and 7.36 ± 0.41μM, respectively.

Room-temperature in-plane ferromagnetism in Co-substituted Fe5GeTe2 investigated by magnetic x-ray spectroscopy and microscopy

Abstract The exploration of two-dimensional (2D) van der Waals ferromagnets has revealed intriguing magnetic properties with significant potential for spintronics applications. In this study, we examine the magnetic properties of Co-doped Fe5GeTe2 using x-ray photoemission electron microscopy (XPEEM) and x-ray magnetic circular dichroism (XMCD), complemented by density functional theory calculations. Our XPEEM measurements reveal that the Curie temperature ( T C ) of a bilayer of (Co x Fe 1 − x ) 5 − δ GeTe2 (with x = 0.28) reaches ∼300 K—a notable enhancement over most 2D ferromagnets in the ultrathin limit. Interestingly, the T C shows only a small dependence on film thickness (bulk T C ≈ 340 K), in line with the observed in-plane (IP) magnetic anisotropy and robust IP exchange coupling. XMCD measurements indicate that the spin moments for both Fe and Co are significantly reduced compared to the theoretical values. These insights highlight the potential of Co-doped Fe5GeTe2 for stable, high-temperature ferromagnetic applications in 2D materials.

Homochiral Dy2 zero-field single-molecule magnets derived from axial chiral ligands (R)/(S)-octahydro-1,1'-bi-2-naphthyl phosphate.

The construction of homochiral zero-field single-molecule magnets (SMMs), especially with axial chiral ligands, remains a great challenge. Herein the first examples of homochiral Dy(III) Schiff base complexes based on axial chiral ligands (R)/(S)-5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthyl phosphate (R-HL/S-HL), [Dy2(R-L/S-L)2(LSchiff)2(H2O)(MeOH)]·2MeOH·CH2Cl2·2MeCN·2H2O (R-1/S-1) [H2LSchiff = (E)-N'-(5-fluoro-2-hydroxybenzylidene)pyrazine-2-carbohydrazide], were synthesized at room temperature, which show ferromagnetic coupling and act as zero-field SMMs, with a Ueff/k value of 61 K at 0 Oe. Ab initio calculations were used to explain their magnetic interaction and magnetic relaxation properties. Furthermore, the magnetic circular dichroism (MCD) spectra of R-1/S-1 revealed that they display obvious magneto-optical effects.

Design of an abiotic unimolecular three-helix bundle.

Starting from the solid state structure of C 3-symmetrical homochiral parallel trimolecular bundle of three aromatic helices held together by intermolecular hydrogen bonds, we have used simple rational principles and molecular modelling to design a similar heterochiral structure where one helix had an opposite orientation and handedness. A rigid and a flexible linker to connect these helices and transform the bundle into a unimolecular object were designed and synthesized. Model sequences with two helices and one linker were then prepared. Their conformations were investigated in solution by nuclear magnetic resonance and circular dichroism, in the solid state by X-ray crystallography, and by molecular dynamics simulations, overall supporting the initial design. A final 6.9 kDa unimolecular three-helix bundle was then prepared using a fragment condensation approach. Solution studies support the formation of the targetted tertiary fold in the case of the rigid linker, thereby validating the overall approach.

Aromatic-aromatic interactions drive fold switch of GA95 and GB95 with three residue difference.

Proteins typically adopt a single fold to carry out their function, but metamorphic proteins, with multiple folding states, defy this norm. Deciphering the mechanism of conformational interconversion of metamorphic proteins is challenging. Herein, we employed nuclear magnetic resonance (NMR), circular dichroism (CD), and all-atom molecular dynamics (MD) simulations to elucidate the mechanism of fold switching in proteins GA95 and GB95, which share 95% sequence homology. The results reveal that long-range interactions, especially aromatic π-π interactions involving residues F52, Y45, F30, and Y29, are critical for the protein switching from a 3α to a 4β + α fold. This study contributes to understanding how proteins with highly similar sequences fold into distinct conformations and may provide valuable insights into the protein folding code.