Magnetic Coupling Constants Research Articles

Strong coupling constants of doubly heavy baryons with vector mesons in QCD

Using the most general form of the interpolating current for baryons, the strong electric and magnetic coupling constants of light vector mesons rho and K^* with doubly heavy baryons are computed within the light-cone sum rules. We consider 2- and 3-particle distribution amplitudes of the aforementioned vector mesons. The obtained results can be useful in the analysis of experimental data on the properties of doubly heavy baryons conducted at LHC.

Tuning structural-transformation temperature toward giant magnetocaloric effect in MnCoGe alloy: A theoretical study

We propose a new model and scheme to consider the effect of structural transformation on magnetocaloric properties of Mn1-xCuxCoGe. The magnetic exchange coupling constants are estimated from first-principles calculations based on density functional theory. The magnetic phase diagram is semi-quantitatively reproduced by using mean-field approximation. The giant isothermal magnetic entropy change with the magnetostructural coupling of Mn0.89Cu0.11CoGe alloy is well reproduced by using the modified Potts model. The enhancement of magnetostructural coupling on the isothermal magnetic entropy change strongly depends on the condition of the magnetic phase transition temperature of orthorhombic and hexagonal phases.

Magnetic Coupling in a Tris-hydroxo-Bridged Chromium Dimer Occurs through Ligand Mediated Superexchange in Conjunction with Through-Space Coupling.

Quantum chemistry can explain and predict many properties of molecules and materials. However, there are some systems, among which are magnetic systems, that remain a challenge for all electronic structure methods. The tris-hydroxo-bridged chromium dimer, known as Kremer's dimer, contains two antiferromagnetically coupled chromium(III) metal ions and provides a classic example of a magnetic molecular system that poses a challenge for computational quantum chemistry. In this study we show that combining multiconfiguration pair-density functional theory with large-active-space density matrix renormalization group wave functions can predict the correct spin-state ordering, energy spacing, and magnetic coupling constant. We also use the unpaired electron density to analyze the superexchange contribution. This methodology offers promise for revolutionary rational design of molecular magnets.

A new CuII-dinuclear paddlewheel complex. Structural and electronic properties

A new paddlewheel dinuclear CuII complex [Cu2(HL)4(MeOH)2](MeOH)4, Cu2-PW was obtained using the 3,5-di‑tert‑butyl‑salicylic acid as a ligand (H2L). The Cu2-PW crystallizes in the monoclinic P2/c space group having a Cu…Cu distance of 2.5727(17) Å. The hydrogen bonds between coordinated and solvate methanol molecules link the structure into a pseudo-one-dimensional array with a Cu…Cu interdimer distance of 9.180(5) Å. Temperature dependence of magnetic susceptibilities revealed a strong antiferromagnetic interaction between the two CuII ions (J = −323 cm−1). DFT calculations showed that the strong antiferromagnetic behavior is originated from magnetic orbital centered only on CuII cations and carboxy oxygen atoms, with a calculated exchange magnetic coupling constant of J12= -311 cm−1. Time-dependent calculations were also performed to characterize the main electronic transition involved in the two well-defined maxima observed in solid-state. The results show that the maximum at 695 nm corresponds to d-d and carboxylate intraligand transitions, while the maximum centered at 320 nm was assigned to phenyl to carboxylate ILCT transition. The shoulder located around 400 nm corresponds to MLCT transition from HL− ligand to CuII center. In our knowledge, this is the first time that a copper paddlewheel complex with the salicylic ligand is studied using the hole-electron method to give a univocal assignment for the UV–vis spectrum.

Energies, radial expectation values, hyperfine structures of the ground state and highly excited states for C and O2+

The Rayleigh–Ritz variational method with multiconfiguration interaction wave functions is used to calculate energies, radiative transitions and radial expectation values of the [Formula: see text] [Formula: see text] ground state and the [Formula: see text], [Formula: see text], [Formula: see text] highly excited states of C and [Formula: see text]. Hyperfine structure parameters and magnetic coupling constants of these states are also calculated in this work. The present calculations agree well with theoretical and experimental values available in the literature. Other data not reported in the literature are expected to offer valuable benchmarks for future research.

Theoretical prediction of magnetic exchange coupling constants from broken-symmetry coupled cluster calculations.

Exchange coupling constants (J) are fundamental to the understanding of spin spectra of magnetic systems. Here, we investigate the broken-symmetry (BS) approaches of Noodleman and Yamaguchi in conjunction with coupled cluster (CC) methods to obtain exchange couplings. J values calculated from CC in this fashion converge smoothly toward the full configuration interaction result with increasing level of CC excitation. We compare this BS-CC scheme to the complementary equation-of-motion CC approach on a selection of bridged molecular cases and give results from a few other methodologies for context.

Parameterization of dilute Ising model for iron-containing lanthanum gallate and aluminate solid solutions based on first-principles calculations

Calculations of the cubic models of two solid solutions LaGa0.5Fe0.5O3 and LaAl0.5Fe0.5O3 have been performed within the hybrid density functional theory. Multiple configurations have been considered for the solid solutions resulting from a different distribution of Fe atoms over the p-metal (Ga or Al) positions accounting for different spin orientation for Fe atoms themselves. It was demonstrated that 27 structures for both LaGa0.5Fe0.5O3 and LaAl0.5Fe0.5O3 should be treated to account for all the possible configurations in case of cubic 2 × 2 × 2 supercell. Optimized geometry, energy, and electron properties were calculated for all the obtained configurations. Statistical weights and probabilities were estimated for each symmetry non-equivalent configuration of the solid solutions within the canonical ensemble. A new parameterization for the dilute Ising model has been proposed. In this model, we account for non-magnetic contributions, which are absent in the simple Ising model, using the lattice approach based on the concept of interchange energy. Two model parameters (the magnetic coupling constant and interchange energy) were fitted to the calculated total energies of all considered configurations of both solid solutions. The dilute Ising model confirmed the benefit of Fe-clustering in doped lanthanum gallate against aluminate. Different signs of the estimated interchange energy enable us to explain the reasons for such differences.

Effects of carboxylic acid auxiliary ligands on the magnetic properties of azido-Cu(II) complexes: A density functional theory study

The magnetic properties of the azide copper complex [Cu2(dpyam)2(μ1,1-N3)2(O2CCH3)2] were studied using the density functional theory-broken symmetry methodology under different functional methods and basis sets. The magnetic coupling constant between paramagnetic centres was calculated as 36.75 cm−1, which agreed with the experimental value of 31.9 cm−1. Accordingly, the calculations at the B3LYP/def2-TZVP level could describe the magnetic properties of the azide copper complex accurately. To study thoroughly the effect of carboxylic acid auxiliary ligands in azido-Cu(II) systems, acetas were deleted from the auxiliary ligands(1) and replaced by H2O-(2), HCOO-(3), CH3COO-(4), C2H5COO-(5), and C6H5COO-(6), yielding six research models. With the increased electron donating effect on carboxylic acid substituents, the ferromagnetic interaction between the paramagnetic centres was enhanced, whereas the contribution of the antiferromagnetic interaction was reduced. The parameters ρHS2-ρBS2,Sab2, and (ε1-ε2)2 can be extended to other binuclear complexes for the study of magneto-structural correlation.

Role of electron correlation in the P,T -odd effects of CdH: A relativistic coupled-cluster investigation

We investigate the parity ($\mathcal{P}$) and time-reversal ($\mathcal{T}$) symmetry violating effects in the CdH molecule and perform the relativistic coupled-cluster calculation of the molecular parameters- $E_\text{eff}$, $W_\text{s}$ and $W_\text{M}$ related to the electric dipole moment of electron (eEDM) interaction, the scalar-pseudoscalar (S-PS) nucleus-electron neutral current coupling and the nuclear magnetic quadrupole moment (MQM) interaction with electrons, respectively. We also compute the molecular dipole moment and the magnetic hyperfine structure coupling constant of CdH. The value of $E_\text{eff}$, $W_\text{s}$ and $W_\text{M}$ obtained by us in the said molecule are 12.2 GV/cm, 14.0 kHz and $0.82\times$10$^{33}$ Hz/e cm$^2$, respectively, within an uncertainty of 10\%. Furthermore, we study the trend of electron-correlation in the computed properties of CdH and that of the $\mathcal{P,T}$-odd parameters in the group-12 monohydrides (i.e., ZnH, CdH, and HgH).

Long- and short-range magnetism in the frustrated double perovskite Ba2MnWO6

The structural and magnetic properties of the face-centered cubic double perovskite Ba2MnWO6 were investigated using neutron powder diffraction, DC-magnetometry, muon spin relaxation and inelastic neutron scattering. Ba2MnWO6 undergoes Type II long-range antiferromagnetic ordering at a Neel temperature of 8(1) K with a frustration index, f = 8. Inelastic neutron scattering was used to identify the magnetic coupling constants J1 and J2, which were found to equal -0.080 meV and -0.076 meV respectively. This indicated that both of the magnetic coupling constants were antiferromagnetic with similar magnitudes, which is in contrast to other known 3d metal double perovskites Ba2MWO6. Above the Neel temperature, muon spin relaxation measurements and inelastic neutron scattering techniques identify a short-range correlated magnetic state that is similar to that observed in the archetypical face-centered cubic lattice antiferromagnet MnO.

Search for octupole-deformed actinium isotopes using resonance ionization spectroscopy

In-source resonance ionization spectroscopy of the neutron-rich actinium isotopes $^{225\ensuremath{-}229}\mathrm{Ac}$ has been performed at the ISAC facility in TRIUMF, probing a $^{2}D_{3/2}\ensuremath{\rightarrow}^{4}P_{5/2}^{\ensuremath{\circ}}$ atomic transition. New data on the magnetic dipole moments and changes in mean-square charge radii $\ensuremath{\delta}\ensuremath{\langle}{r}^{2}\ensuremath{\rangle}$ of $^{226,228,229}\mathrm{Ac}$ have been obtained. The comparison of the measured isotope shifts and magnetic dipole coupling constants $a(^{4}P_{5/2}^{\ensuremath{\circ}})$ of $^{225,227}\mathrm{Ac}$ with a high-resolution data set is used to identify systematic uncertainties on the deduced $\ensuremath{\delta}{\ensuremath{\langle}{r}^{2}\ensuremath{\rangle}}^{A,215}$ and magnetic dipole moment values. The charge radii odd-even staggering is evaluated for the odd-$N$ isotopes, showing that $^{226}\mathrm{Ac}$ has an inverted odd-even staggering that might be linked with a reflection-asymmetric shape. Comparison of the magnetic dipole moments of $^{225,227,229}\mathrm{Ac}$ with Nilsson-model estimates supports the assumption of octupole deformation in isotopes $^{225,227}\mathrm{Ac}$ and its gradual decrease toward isotope $^{229}\mathrm{Ac}$. The changes in mean-square charge radii are compared to self-consistent calculations employing multiple modern energy density functionals: SLy5s1, BSk31, and DD-MEB1. For SLy5s1 in particular, self-consistent time-reversal breaking calculations of odd-odd nuclei incorporating finite octupole deformation are reported for the first time. For these calculations, the overall best agreement is obtained when the octupole degree of freedom is taken into account.

Coupling Constants, High Spin, and Broken Symmetry States of Organic Radicals: an Assessment of the Molecules-in-Molecules Fragmentation-Based Method.

We extend the application of our multilayer molecules-in-molecules (MIM) fragmentation-based method to the study of open-shell systems, particularly organic radicals. A test set of organic mono-, di- and polyradicals with a wide range in size, containing up to 360 atoms, was investigated. Total energies computed with MIM using density functional theory (DFT) were compared with full, unfragmented energies to assess the performance of MIM and to develop a systematic protocol for the treatment of large radical systems. More specifically, a two-layer (MIM2) model with a fragmentation scheme along the backbone involving covalently bonded dimers, trimers, or tetramers was considered, with DFT at a smaller basis set serving as the low level of theory. The MIM method was evaluated on the high-spin state and several possible broken-symmetry (BS) states for di- and polyradicals. When relevant spin-spin interactions were considered, the errors in total energies were less than 1 kcal mol-1. In addition, the applicability of MIM2 was extended to predict the intersite magnetic exchange coupling constants (J), which were compared with reference values. Further, since the energy levels derived from Hamiltonian diagonalization are physically more meaningful, the calculated J values estimated from the BS-DFT methodology were used to obtain the lower spin state energies of the polyradicals. The difference in calculated total energies of the lower spin state between full and MIM2 lie within 1 kcal mol-1 in the majority of these cases. Our rigorous, quantum chemical study demonstrates that MIM can be successfully applied to the study of large organic radicals reliably and accurately within the framework of BS-DFT.

A cyanide-bridged FeIII-MnII heterobimetallic one-dimensional coordination polymer: synthesis, crystal structure, experimental and theoretical magnetism investigation.

A new cyanide-bridged FeIII-MnII heterobimetallic coordination polymer (CP), namely catena-poly[[[N,N'-(1,2-phenylene)bis(pyridine-2-carboxamidato)-κ4N,N',N'',N''']iron(III)]-μ-cyanido-κ2C:N-[bis(4,4'-bipyridine-κN)bis(methanol-κO)manganese(II)]-μ-cyanido-κ2N:C], {[FeMn(C18H12N4O2)(CN)2(C10H8N2)2(CH3OH)2]ClO4}n, (1), was prepared by the self-assembly of the trans-dicyanidoiron(III)-containing building block [Fe(bpb)(CN)2]- [bpb2- = N,N'-(1,2-phenylene)bis(pyridine-2-carboxamidate)], [Mn(ClO4)2]·6H2O and 4,4'-bipyridine, and was structurally characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography and powder X-ray diffraction (PXRD). Single-crystal X-ray diffraction analysis shows that CP 1 possesses a cationic linear chain structure consisting of alternating cyanide-bridged Fe-Mn units, with free perchlorate as the charge-balancing anion, which can be further extended into a two-dimensional supramolecular sheet structure via inter-chain π-π interactions between the 4,4'-bipyridine ligands. Within the chain, each MnII ion is six-coordinated by an N6 unit and is involved in a slightly distorted octahedral coordination geometry. Investigation of the magnetic properties of 1 reveals an antiferromagnetic coupling between the cyanide-bridged FeIII and MnII ions. A best fit of the magnetic susceptibility based on the one-dimensional alternating chain model leads to the magnetic coupling constants J1= -1.35 and J2 = -1.05 cm-1, and the antiferromagnetic coupling was further confirmed by spin Hamiltonian-based density functional theoretical (DFT) calculations.

Jx: An open-source software for calculating magnetic interactions based on magnetic force theory

We describe our newly-developed open-source software, named by Jx, to perform magnetic force linear response calculations. Jx is a user-friendly and efficient tool to calculate magnetic interaction in solids and molecules. Without supercell calculation, it computes both short- and long-range interactions. It is also possible to calculate an orbital-resolved matrix form of magnetic couplings. Functionality and formalism are presented with examples. The program architecture and parallel algorithm are also described. Program summaryProgram Title: JxProgram Files doi:http://dx.doi.org/10.17632/kg5x95gwgj.1Licensing provisions: LGPLProgramming language: JuliaNature of problem: The first-principles estimation of magnetic interaction in solids and molecules.Solution method: Calculate the magnetic coupling constant based on magnetic force response theory.

Experimental and quantum computational study of two new bridged copper(II) coordination complexes as possible models for antioxidant superoxide dismutase: Molecular structures, X-band electron paramagnetic spectra and cryogenic magnetic properties

In the present study, we use a dual approach comprising experimental and quantum computational studies of two new bridged copper(II) coordination complexes with NNO donor ligands, viz., [Cu2(μ-sulfato)(L)2(2H2O)]·1.5H2O (1) and [Cu2(μ-succinato)(L)(HL)(H2O)]ClO4 (2), where HL/L = N′-[(E)-pyridin-2-ylmethylidene]benzohydrazide, have been synthesized and characterized using various physico-chemical techniques. Both complexes are structurally characterized using single crystal X-ray diffraction studies. The distances between two copper centers are 3.270(2) Å and 3.178(1) Å, for 1 and 2, respectively. On the basis of quantum computational DFT study, electronic excitations involve transitions mainly from metal-ligand bonding MO’s to the β-LUMO within the dominant Cu atom exhibiting dxy character and to the β-LUMO+1. EPR spectra for these polycrystalline samples were determined for the copper(II) hyperfine structures as well their zero-field splitting which are appropriate for the triplet state of such dimers. Cryomagnetic behavior is consistent with weak antiferromagnetic interactions between the Cu(1)⋯Cu(2) centers in both complexes. The magnetic exchange coupling constant (J) between the Cu(1)⋯Cu(2) centers for 1 and 2 were determined to be J = −1.50(1) and J = −7.7(1)cm−1, respectively. CH⋯π, π⋯π, and lone pair⋯π interactions which have gained attention and their role in bimolecular structure analysis has been recognized. In addition, antioxidant superoxide dismutase activity measurements have showed that homodinuclear complexes give significant scavenging effects against superoxide free radicals. Complex 2 is more antioxidant superoxide dismutase active than 1.

Theoretical Investigation of the Electronic Structure and Magnetic Properties of Oxo-Bridged Uranyl(V) Dinuclear and Trinuclear Complexes.

The uranyl(V) complexes [UO2(dbm)2K(18C6)]2 (dbm = dibenzoylmethanate) and [UO2(L)]3(L = 2-(4-tolyl)-1,3-bis(quinolyl)malondiiminate), exhibiting diamond-shaped U2O2 and triangular-shaped U3O3 cores respectively with 5f1-5f1 and 5f1-5f1-5f1 configurations, have been investigated using relativistic density functional theory (DFT). The bond order and QTAIM analyses reveal that the covalent contribution to the bonding within the oxo cores is slightly more important for U3O3 than for U2O2, in line with the shorter U-O distances existing in the trinuclear complex in comparison to those in the binuclear complex. Using the broken symmetry (BS) approach combined with the B3LYP functional for the calculation of the magnetic exchange coupling constants (J) between the magnetic centers, the antiferromagnetic (AF) character of these complexes was confirmed, the estimated J values being respectively equal to -24.1 and -7.2 cm-1 for the dioxo and trioxo species. It was found that the magnetic exchange is more sensitive to small variations of the core geometry of the dioxo species in comparison to the trioxo species. Although the robust AF exchange coupling within the UxOx cores is generally maintained when small variations of the UOU angle are applied, a weak ferromagnetic character appears in the dioxo species when this angle is higher than 114°, its value for the actual structure being equal to 105.9°. The electronic factors driving the magnetic coupling are discussed.

Synthesis, structural and DFT analysis of a binuclear nickel(II) complex with the 1,4-bis[2-[2-(diphenylphosphino)benzylidene]]phthalazinylhydrazone ligand

In this work we present the synthesis, and experimental and theoretical analysis of a binuclear nickel(II) complex coordinated to a new phthalazine dihydrazone-based ligand. Single-crystal X-ray diffraction analysis of the metal complex shows that the coordination geometry around each nickel(II) atom is distorted octahedral. DFT calculations predict that the magnetic exchange coupling constant of the binuclear nickel(II) complex is predominantly anti-ferromagnetic.

Magnetic properties of solid solutions LaGaxFe1-xO3 and LaAlxFe1-xO3: first-principles study

We used hybrid density functional theory to investigate 50% cubic solid solutions based on Fe-doped LaGaO3 and LaAlO3. The supercell composed of 8 primitive cells was used. All the possible configurations of the solid solutions considering specific magnetic ordering were split into Symmetry Independent Classes (SICs). Optimized geometry, energy and electron properties were calculated for one representative structure of each class. Magnetic coupling constants were obtained using Ising model. Estimated temperature dependences of the magnetic moment demonstrated qualitatively differences for considered solid solutions.

Crystal structure and magneto-structural investigation of alkoxido bridged dinuclear Fe(III) complexes with 1,3-oxazolidine ligands

Four 1,3-oxazolidine based ligands (H2L1−H2L4) were synthesized in solvent-free condition from the reaction of amino alcohols (2-amino-2-(hydroxymethyl)-1,3-propanediol or 2-amino-2-ethyl-1,3-propanediol) and 2-acetylpyridine or 2-pyridinecarboxaldehyde at 110 °C. Four new dinuclear Fe(III) complexes, [Fe2(HL1)(N3)4] (1), [Fe2(HL2)(N3)4] (2), [Fe2(HL3)(N3)4] (3) and [Fe2(HL4)(N3)4] (4), were synthesized with a similar procedure by the reaction of H2L1–4, Fe(NO3)3·9H2O and NaN3 in 1:1:2 molar ratios in methanol. The ligands and complexes were characterized by elemental analysis and spectroscopic methods. The structure of complexes was solved by single-crystal X-ray diffraction analysis which showed complexes 1–4 to be alkoxido-bridged dinuclear Fe(III) complexes. The structural studies indicated that the crystal structure of 2, 3 and 4 consist of a centrosymmetric dinuclear Fe(III) complexes while the asymmetric unit in 1 consists of two halves of the two independent molecules. The Fe(III) ions have similar coordination environments (cis-FeN4O2) in all of 1–4 which can be described as distorted octahedral geometry. The 1,3-oxazolidine ligands act as mononegative tridentate N2O-donor ligand in 1–4. Two azide groups are also coordinated to each Fe(III) ion as terminal monodentate ligands. The alcoholic arms of the 1,3-oxazilidine ligands act as bridging groups between Fe(III) ions and the Fe⋯Fe distances through these bridges are in the range of 3.157–3.198 Å. Magnetic studies in 2–300 K range reveal antiferromagnetic interactions between the Fe(III) ions with values for the magnetic coupling constants in the range −9.4 cm−1 to −9.7 cm−1, with H = −2J(S1S2).

The annealing effect on memory state stability and interlayer coupling in perpendicular magnetic tunnel junctions with ultrathin MgO barrier

Abstract Perpendicular magnetic tunnel junctions (p-MTJs) attract great interest because of their excellent performance in spin-transfer-torque magnetic random access memories (STT-MRAMs). The annealing process is critical to achieve the required structural and magnetic properties, therefore obtaining high perpendicular tunneling magnetoresistance (p-TMR) and lower switching current. In this work, the CoFeB/MgO/CoFeB-based p-TMR stack was prepared and a high p-TMR value of 155.9% was obtained from CIPT. The p-MTJs were patterned with pillar sizes ranging from 50 nm to 1000 nm and were annealed upon different annealing temperatures (TA) of 300 and 340 °C. The resistance at parallel (RP) and antiparallel (RAP) state in p-MTJs was obtained upon the application of a ±30 mT perpendicular magnetic field, where the angle of magnetization between storage and reference layer at memory state, θP and θAP, were derived from the P and AP resistance ratios with and without magnetic field. The condition θP = θAP of about 63.5° was found in as-deposited samples, indicating a ferromagnetic interlayer coupling between storage and reference layers, where θP = 0° and θAP = 180° at TA = 300 °C and 340 °C demonstrate a stable memory state. The stability of the resistance state was modeled by considering the evolution of effective perpendicular magnetic anisotropy (Keff) and interlayer coupling constant (J), showing a method to evaluate the ratio of Keff/J via the memory state resistance characterization, where the Keff/J of about −1.26 was obtained in our as-deposited samples. Our study assesses the effect of TA on the θP and θAP and supplies the method to enhance the stability through the optimization of perpendicular magnetic anisotropy and interlayer coupling, so to better control the performance of p-MTJ-based STT-MRAMs.