Spin Hamiltonian Parameters Research Articles

ESR and magnetic studies of nickel ions doped P2O5–ZnO–Na2O glassy system

We prepared 42P2O5–40ZnO–(18-x)Na2O–(x)NiO glasses doped with xNiO where 1 ≤ x ≤ 6 mol.%. The optical absorption indicates that the nickel ions exist in both sites tetrahedral and octahedral as the concentration of NiO is increased. This investigation has provided the increasing degree of disorder in the glass network at higher concentrations of NiO. The magnetic characteristics investigated by two techniques electron spin resonance (ESR) spectra and magnetic properties using vibrating sample magnetometer (VSM) at room temperature. The ESR spectra exhibit resonance signal without hyperfine interaction of all the investigated glass samples. It is found that Ni2+ ions were in octahedral sites and it has 3A2g as ground state. The spin-Hamiltonian parameters are evaluated from the ESR spectra and we found a variation of and with different nickel concentration. Interesting results are found for the number of Ni2+ ions participating in resonance (N) and paramagnetic susceptibility (χ). The magnetic properties were performed at room temperature under an applied field of 20 kOe and the hysteresis loops of the powders were extracted for all the considered samples.

Cobalt(III) complex of substituted nalidixic acid: Synthesis, characterization (IR, UV, EPR), single crystal X-ray, antimicrobial activity, Hirshfeld surface analysis and molecular docking

The mixed–ligand title complex, [Co(nal)2(py)2].4H2O (Hnal=nalidixic acid, py=pyridine), was synthesized. Its structural properties were characterized by X–ray diffraction technique (XRD) and elemental analysis. The spectroscopic properties are investigated by Fourier transform infrared spectroscopy (FT–IR), UV–Vis spectroscopy and EPR spectroscopy. The Co(II) ion has slightly distorted octahedral geometry surrounded by two oxygen atoms of keto and carboxyl groups bonded as chelate from nalidixate, two nitrogen atoms from two pyridine ligands. The monomer are connected by C–H···O and C–H···C interactions to form sheet structures. The FT-IR studies of the complex were commented, focusing on the shifts in the vibrational peaks between the complex form and free nalidixic acid. The powder EPR spectra of Cu(II)-doped complex were investigated at room and at liquid nitrogen temperature. The EPR and UV–Vis spectroscopy studies showed that the unpaired electrons were found in the dx2−y2 orbitals by calculating the spin-Hamiltonian and bond parameters. 2D and 3D Hirshfeld analyses were performed in order to quantify the order and nature of intermolecular interactions in crystal network. Antibacterial activity of complex was studied against S. aureus, B. subtilis, P. aeruginosa, E. coli, C. albicans and A. flavus by using the micro dilution. The optimized complex is docked to 5J9B (S. aerous), 5BMM (E. Coli), 5HTG (C. Albicans), 1ZUV (B. Subtilis), 4F0V (P. aeruginosa) and 4YNU (A. flavus).

Mechanistic basis of substrate–O2 coupling within a chitin-active lytic polysaccharide monooxygenase: An integrated NMR/EPR study

Lytic polysaccharide monooxygenases (LPMOs) have a unique ability to activate molecular oxygen for subsequent oxidative cleavage of glycosidic bonds. To provide insight into the mode of action of these industrially important enzymes, we have performed an integrated NMR/electron paramagnetic resonance (EPR) study into the detailed aspects of an AA10 LPMO-substrate interaction. Using NMR spectroscopy, we have elucidated the solution-phase structure of apo-BlLPMO10A from Bacillus licheniformis, along with solution-phase structural characterization of the Cu(I)-LPMO, showing that the presence of the metal has minimal effects on the overall protein structure. We have, moreover, used paramagnetic relaxation enhancement (PRE) to characterize Cu(II)-LPMO by NMR spectroscopy. In addition, a multifrequency continuous-wave (CW)-EPR and 15N-HYSCORE spectroscopy study on the uniformly isotope-labeled 63Cu(II)-bound 15N-BlLPMO10A along with its natural abundance isotopologue determined copper spin-Hamiltonian parameters for LPMOs to markedly improved accuracy. The data demonstrate that large changes in the Cu(II) spin-Hamiltonian parameters are induced upon binding of the substrate. These changes arise from a rearrangement of the copper coordination sphere from a five-coordinate distorted square pyramid to one which is four-coordinate near-square planar. There is also a small reduction in metal-ligand covalency and an attendant increase in the d(x2-y2) character/energy of the singly occupied molecular orbital (SOMO), which we propose from density functional theory (DFT) calculations predisposes the copper active site for the formation of a stable Cu-O2 intermediate. This switch in orbital character upon addition of chitin provides a basis for understanding the coupling of substrate binding with O2 activation in chitin-active AA10 LPMOs.

Optical applications of copper doped lithium phosphate glasses

Lithium optical phosphate glass materials were prepared by melt-quenching method by using a special composition 65 P2O5 -10 Pb3O4 – 5 ZnO – (20-x) Li2CO3 – x CuO (x = 0, 0.2, 0.4, 0.6, 0.8,1.0).The amorphous nature of prepared glasses is confirmed through X-ray diffraction (XRD) spectra. The increase in densities and decrease in refractive index values with the enhancement of the quantity of Cu2+ ions are observed in these glasses. Morphological study of these glass samples revealed their biomedical applications. Spin–Hamiltonian parameters are evaluated by using Electron paramagnetic resonance (EPR) spectra andthe observed positions of Cu2+ ions are characteristic of tetragonally elongated octahedral sites. Breaking of POP bonds and creating P-O-Cu bonds are noticed in Fourier transform infrared (FTIR) spectra. The optical band gap energy values were decreasing from 2.91−2.89eVas the copper ion content is increased,support the applications of thin films and the transmission spectra reveal the optical applications such as bandpass filter.

Synthesis, crystal structure, spectroscopic (FT-IR, UV–Vis, EPR) and Hirshfeld surface analysis studies of Zn(II)-benzoate coordination dimer

Mixed ligand coordination dimer [Zn2(BA)4(NA)2].(BAH), (BAH=Benzoic acid, NA=nicotinamide), synthesized and its supramolecular architecture was investigated. The structural properties of the coordination dimer were characterized by X-ray diffraction (XRD), elemental analysis, spectroscopic methods (EPR, UV–Vis and FT-IR), thermogravimetric analysis and Hirshfeld surface analysis. The complex crystallized in the monoclinic crystal system and the P21/c space group. Two benzoate anions bind to zinc metals as chelates, while the other two-benzoate anions bridge between two metals. The coordinate environment of the Zn1 atom has a nearly ideal square pyramidal geometry and the τ factor defined by Addison is 0.09. The coordination environment of the Zn2 atom has an extremely distorted (4 + 1) pseudo-square pyramidal geometry and the τ factor was found to be 0.35. Hydrogen bonds and π⋯π weak interactions form a three-dimensional supramolecular structure. IR spectroscopic studies of the complex were performed in the middle IR region, focusing mainly on the characteristic vibrations of benzoic acid and nicotinamide, taking into account ligand functional groups within the complex. The EPR spectra of Cu(II)-doped complex were investigated at room and at liquid nitrogen temperature. As a result of EPR analysis, spin hamiltonian parameters were obtained. In addition, zero field splitting parameters of the dimer-complex was obtained as Dobs = 0.60 cm−1 and E ≈ 0. Thermogravimetric Analysis (TGA) was carried out thermal properties. 2D and 3D Hirshfeld analyses were performed in order to quantify the order and nature of intermolecular interactions in crystal network.

Synthesis and spectroscopic investigations of calcium cadmium phosphate hydrate nanopowders via doping divalent (Mn2+) and trivalent (Fe3+) cations

Calcium Cadmium Phosphate Hydrate (CaCdPH) powders with transition metal ions (Mn2+ & Fe3+) as dopants are synthesized via solid state route. The prepared nanopowders phase was confirmed by using XRD analysis. The surface morphology was analyzed by recording their SEM images. The quantitative chemical analysis of CaCdPH: Mn2+ and CaCdPH: Fe3+ was confirmed from energy dispersive spectroscopy (EDS). From the optical and Electron paramagnetic resonance (EPR) spectra, the site symmetries of CaCdPH: Mn2+ and CaCdPH: Fe3+ are ascribed as distorted octahedral. Various EPR parameters such as spin Hamiltonian parameters (g-value), hyperfine (HF) parameter A, number of spins (N) and paramagnetic susceptibility (χ) are evaluated.

Studies on spin Hamiltonian parameters and local structures for v4+ in BaCl2-BaO-B2O3 glasses at various BaCl2 compositions

ABSTRACT The spin Hamiltonian parameters (SHPs), local structure and their composition dependences for impurity V4+ in xBaCl2-(30–x)BaO-68B2O3-2V2O5 (x = 0, 2, 5, 10 mol%) glasses are theoretically analyzed by using the perturbation formulae of SHPs for octahedral 3d1 clusters with tetragonal compression. The power law composition functions for the relevant quantities (covalency factor N, relative tetragonal compression ratio ρ, core polarisation constant κ and reduction factor H) suitably recur the experimental composition dependences of the SHPs for V4+. N shows the firstly fast and then slow decreasing trend, whereas ρ, κ and H exhibit the firstly fast and then slow increasing tendencies. The above composition dependences can be attributed to the modifications of the local structure and electron cloud distribution near the impurity V4+ due to the doped chlorine in participating in the formation and modification of the glasses network and mixed alkali effect.

Investigation of the Optical Spectra and Spin-Hamiltonian Parameters for Vanadyl in Zinc Phosphate Glass

The optical absorption spectra and spin-Hamiltonian parameters (g factors g||, g⊥, and hyperfine structure constants A||, A⊥ ) of vanadyl in zinc phosphate glass are investigated, using the high-order perturbation formulas for a 3d1 ion in tetragonally compressed octahedra. In the calculations, the required crystal-field parameters are estimated from the superposition model, and the optical absorption bands and spin-Hamiltonian parameters are linked with the tetragonal distortion (characterized by ΔR = R⊥ – R||, where R⊥ and R|| denote the bond lengths perpendicular and parallel to the C4 axis). Based on the calculations, the tetragonal distortion ΔR (≈1.795 A) was obtained, and negative signs of the hyperfine structure constants A|| and A⊥ are suggested.

Machine Learning Magnetic Parameters from Spin Configurations.

Hamiltonian parameters estimation is crucial in condensed matter physics, but is time‐ and cost‐consuming. High‐resolution images provide detailed information of underlying physics, but extracting Hamiltonian parameters from them is difficult due to the huge Hilbert space. Here, a protocol for Hamiltonian parameters estimation from images based on a machine learning (ML) architecture is provided. It consists in learning a mapping between spin configurations and Hamiltonian parameters from a small amount of simulated images, applying the trained ML model to a single unexplored experimental image to estimate its key parameters, and predicting the corresponding materials properties by a physical model. The efficiency of the approach is demonstrated by reproducing the same spin configuration as the experimental one and predicting the coercive field, the saturation field, and even the volume of the experiment specimen accurately. The proposed approach paves a way to achieve a stable and efficient parameters estimation.

Data-driven determination of the spin Hamiltonian parameters and their uncertainties: The case of the zigzag-chain compound KCu4P3O12

We propose a data-driven technique to estimate the spin Hamiltonian, including uncertainty, from multiple physical quantities. Using our technique, an effective model of KCu$_4$P$_3$O$_{12}$ is determined from the experimentally observed magnetic susceptibility and magnetization curves with various temperatures under high magnetic fields. An effective model, which is the quantum Heisenberg model on a zigzag chain with eight spins having $J_1= -8.54 \pm 0.51 \{\rm meV}$, $J_2 = -2.67 \pm 1.13 \{\rm meV}$, $J_3 = -3.90 \pm 0.15 \{\rm meV}$, and $J_4 = 6.24 \pm 0.95 \{\rm meV}$, describes these measured results well. These uncertainties are successfully determined by the noise estimation. The relations among the estimated magnetic interactions or physical quantities are also discussed. The obtained effective model is useful to predict hard-to-measure properties such as spin gap, spin configuration at the ground state, magnetic specific heat, and magnetic entropy.

Two kinds of oxygen vacancies in lithium titaniate doped with copper as detected by EPR

Lithium titanate (Li1+xTi2-xO4) doped with Cu2+ ions was synthesized by sol-gel processing method. The structure and morphology are characterized by X-ray Diffraction (XRD), X-ray Photoemission Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Electron Paramagnetic Resonance (EPR). Spin Hamiltonian parameters describing Zeeman and hyperfine interaction for 63Cu2+ ions were obtained from EPR spectra simulations. The spectra are characteristic for (Cu-VO)0 close-associate pairs consisting of copper replacing Ti4+ ion and an adjacent doubly ionized oxygen vacancy. These oxygen vacancies serve as charge compensators for the substituting copper ions. However, there are additional narrow EPR signals at g = 2.004 in all samples, including the sample of LiTi2O4 without dopant. These signals are ascribed to single-electron trapped oxygen vacancies VO●. Superconductivity was not confirmed down to 4.2 K by magnetic measurements in all samples studied.

Optical and magnetic properties of lanthanide(III) complexes with quercetin-5′-sulfonic acid in the solid state and silica glass

The lanthanide [Ln(QSA)3(H2O)](H2O)5 complexes in the polycrystalline state and embedded in the silica glass, where Ln = La, Pr, Nd, Eu, Sm, Dy, Er, Gd, Ho, Tb, were studied and characterized using spectroscopic methods. The europium complex was additionally studied theoretically based on the DFT approach which provided molecular structure and electron transition assignment. The emission spectra measured at 293 and 77 K proved the transformation of excitation pulses into the phonon energy. The EPR studies of the Er, Gd, Dy and Sm derivatives were used to determine spin Hamiltonian parameters and g – components. The antiferromagnetic interactions were found and the local monoclinic symmetry of the coordination polyhedron was proposed.

EPR spectroscopy of 53Cr monoisotopic impurity ions in a single crystal of yttrium orthosilicate Y2SiO5

The electron paramagnetic resonance spectra of 53Cr monoisotopic impurity ions in yttrium orthosilicate single crystals (Y2SiO5) were studied by electron paramagnetic resonance (EPR) in the X-band. The directions of the principal magnetic axes and the parameters of the effective spin Hamiltonian, which describes magnetic characteristics of the impurity centers of chromium are determined. It is shown that the orientation dependencies of the EPR spectra are described by the second-order spin Hamiltonian corresponding to the rhombic symmetry of the local crystal field acting on the impurity ion. It was assumed that the g-tensor and A-tensor describing the Zeeman energy of electron levels in a magnetic field and the hyperfine interaction of electron and nuclear spins are isotropic, and the entire anisotropy of the EPR spectra is due to the anisotropy of the D-tensor, which describes the fine structure of electron levels in crystal electric field. A strong dependence of the probability of forbidden transitions between hyperfine sublevels of electron levels on the orientation of an external magnetic field is established. Moreover, for some orientations, the probability of forbidden transitions becomes comparable to the probability of allowed transitions.

Investigations of crystal-field energy levels and microscopic spin-Hamiltonian parameters of Mn4+ ions in pyrochlore hosts Y2Ti2O7 and Y2Sn2O7

We investigate the crystal-field energy levels and the microscopic origin of spin-Hamiltonian parameters (SHPs), i.e. g-factors and zero-field splitting parameter D, for the ground state 4A2g(4F) of Mn4+ impurity ions at trigonal sites in host pyrochlores, Y2Ti2O7 and Y2Sn2O7. The total Hamiltonian includes the electrostatic and crystal-field (CF) Hamiltonians, and the magnetic interactions, i.e. spin-orbit, spin-spin, spin-other-orbit, and orbit-orbit couplings. The calculations are performed under the complete diagonalization method and microscopic spin-Hamiltonian (CDM/MSH) program. The calculated CF levels agree reasonably well with the observed energy levels for Mn4+ ions in these compounds. The SHPs are evaluated with the CDM/MSH wave functions as well as by a perturbation loop theory method (PLTM). The g-factors of Mn4+ in Y2Ti2O7 and Y2Sn2O7 using PLTM are close to those evaluated by CDM, while the PLTM value of D shows appreciable difference with the CDM value. This evidences that the g-factors depend predominately on the lower states, while the higher energy states significantly affect the D value. The contributions of spin-spin, spin-other-orbit, and orbit-orbit couplings to the CF energy levels and the SHPs are discussed.

Electronic Structure and Magnetic Properties of a Titanium(II) Coordination Complex.

Stable coordination complexes of TiII (3d2) are relatively uncommon, but are of interest as synthons for low oxidation state titanium complexes for application as potential catalysts and reagents for organic synthesis. Specifically, high-spin TiII ions supported by redox-inactive ligands are still quite rare due to the reducing power of this soft ion. Among such TiII complexes is trans-[TiCl2(tmeda)2], where tmeda = N,N,N',N'-tetramethylethane-1,2-diamine. This complex was first reported by Gambarotta and co-workers almost 30 years ago, but it was not spectroscopically characterized and theoretical investigation by quantum chemical theory (QCT) was not feasible at that time. As part of our interest in low oxidation state early transition metal complexes, we have revisited this complex and report a modified synthesis and a low temperature (100 K) crystal structure that differs slightly from that originally reported at ambient temperature. We have used magnetometry, high-frequency and -field EPR (HFEPR), and variable-temperature variable-field magnetic circular dichroism (VTVH-MCD) spectroscopies to characterize trans-[TiCl2(tmeda)2]. These techniques yield the following S = 1 spin Hamiltonian parameters for the complex: D = -5.23(1) cm-1, E = -0.88(1) cm-1, (E/D = 0.17), g = [1.86(1), 1.94(2), 1.77(1)]. This information, in combination with electronic transitions from MCD, was used as input for both classical ligand-field theory (LFT) and detailed QCT studies, the latter including both density functional theory (DFT) and ab initio methods. These computational methods are seldom applied to paramagnetic early transition metal complexes, particularly those with S > 1/2. Our studies provide a complete picture of the electronic structure of this complex that can be put into context with the few other high-spin and mononuclear TiII species characterized to date.

Electron paramagnetic resonance and optical properties of Cu+2 in PbO-Li2O-As2O3-B2O3 glasses

The room temperature electron paramagnetic resonance (EPR) and optical absorption studies of PbO-Li2O-As2O3-B2O3 glasses have been done by introducing a transition metal ion Cu+2 ion as a spin probe with fixed mole% in the given glass composition. Glasses containing transition metal (TM) ion give the information of site symmetry around the Cu+2 ion of the host glass. The EPR spectra of Cu+2 in all glass samples recorded in the X-band frequency (9.1–9.7 GHz) have similar features. The spin-Hamiltonian parameters have been calculated; the observed values are g|| > g⊥ > ge and A|| > A⊥. It suggests that the site symmetry around Cu+2 ion is tetragonal distorted octahedral and the ground state of Cu+2 is dx2-y2 (2B1g) orbital. The Cu+2 ion is coordinated with six ligand atoms in a distorted octahedron site symmetry. The optical absorption spectra exhibit a broadband corresponding to d-d transition bonds of Cu+2 ion. Calculated bonding parameters suggest the covalent nature of in-plane σ-bonding (α2) and pure ionic nature for out-of-plane (β2) and in-plane π-bonding (β12). This data is correlated with the theoretical optical basicity (Λth) values, and it is observed that the Γσ value increases whereas Γπ values decrease with increasing Λth.

Theoretical studies of the spin Hamiltonian parameters and local structures for WO3 doped Zn3(PO4)2ZnO nanopowders

The spin Hamiltonian parameters (SHPs) and the local structures for impurity W5+ in the Zn3(PO4)2ZnO nanopowders doped with WO3 under different concentrations are theoretically investigated using the perturbation calculations of these parameters. The exponential functions of the related quantities (cubic field parameter Dq, covalency factor N, relative tetragonal compression ratio τ and core polarisation constant κ) of concentration x with totally four adjustable coefficients a, b, c and d are adopted to fit the concentration dependences of the experimental d-d transition bands and SHPs. The impurity W5+ centres demonstrate moderate tetragonal compression ratios τ (∼3.1%) due to the Jahn–Teller effect. With the increase of WO3 concentration, Dq and N show moderately decreasing rules, while τ and κ exhibit slightly and moderately increasing tendencies with x, respectively. The mechanisms of the above concentration dependences of these quantities are analysed from the modifications of the local crystal-field strength and electron cloud density around the impurity W5+ with the variation of x. Present theoretical studies would be useful to the exploration of the structural properties and optical applications for WO3 doped Zn3(PO4)2ZnO nanopowders.

Recombination luminescence of X-ray induced paramagnetic defects in BaY2F8

Recombination luminescence (RL) and RL-detected electron paramagnetic resonance (RL-EPR) in BaY2F8 single crystal has been investigated after irradiation with X-rays at low temperature. The recombination process, which lasts for several hours at 4 K, results in several broad bands in the RL spectrum. RL-EPR spectra show pronounced angular dependences on crystal orientation relative to external magnetic field. Based on the determined spin-Hamiltonian parameter values the recombination centres have been proposed to be F-type electron and self-trapped hole (VK) centres.

Efficacy of copper ions on lithium ion conductivity, electron hopping, optical band gap, metallization criterion and morphology of Li2O-B2O3-P2O5 glasses

The melt quenching process is adopted in fabricating the glass system 10Li2O-60B2O3-(30-x)P2O5: xCuO (0 ≤ x ≤ 2.5 mol%, where x = 0, 0.5, 1.0, 1.5, 2.0 and 2.5). The specimens are analyzed by X-ray diffraction (XRD), optical absorption, emission spectra, electron spin resonance (ESR) spectra, Fourier transform infrared (FTIR) studies and dielectric investigations. XRD reveals the glassy temperament of specimens. Optical absorption spectra exhibited bands due to Cu2+ ions. ESR spectra exhibited the peaks due to copper ions occupying the octahedral positions. Spin-Hamiltonian parameters of glasses judged the escalating ionic character of specimens with a rise in content of dopant. FTIR displayed traditional bands corresponding to borate and phosphate groups. Dielectric parameters like dielectric constant (ε′), loss (tanδ) and a.c. conductivity (σac) increase with a rise in the quantity of dopant. All results brace that specimen C25 (sample doped with 2.5 mol% of CuO) has the highest semiconducting nature.

Optically Detected Magnetic Resonance Spectroscopy in Silicon Carbide using Temperature Sweep

Optically detected magnetic resonance with temperature sweep is developed using the temperature dependence of the spin Hamiltonian parameters of paramagnetic color centers in silicon carbide. The detection is based on natural optical alignment of spin level populations over a wide temperature range including room temperature and on the change of these populations during level anti-crossing or cross-relaxation processes.