Zero-field Splitting Of Ground State Research Articles

Origin and designing of large ground-state zero-field splitting of color centers in diamond

Origin and designing of large ground-state zero-field splitting of color centers in diamond

Origin and designing of large ground-state zero-field splitting of color centers in diamond

Origin and designing of large ground-state zero-field splitting of color centers in diamond

Heterometallic Co–Sr −2,3-pyridinedicarboxylate complex and its related perovskite oxide: Synthesis, structural characterization and magnetic properties

A new heterometallic complex {[CoSr(2,3-pdc)2(H2O)5]3H2O}n (1), where 2,3-H2pdc stands for 2,3-pyridinedicarboxylic acid, has been synthesized and investigated by single crystal X-Ray diffractometry, IR spectroscopy and thermal analysis. The compound is self-organized in a polymeric structure forming a 2D framework. The 2,3-pyridinedicarboxylic acid is fully deprotonated performing several types of coordination: monodentate, bridging chelating, bidentate bridging. Thermal decomposition of the heterometallic 2,3-pyridinedicarboxylate 1 leads to the formation of a perovskite type oxide of brownmillerite series, 2, with 20.8 % yield. Magnetic studies of 1 show the paramagnetic behavior of Co(II) ions with a significant influence of a ground state zero-field splitting at low temperatures. Variable field and temperature magnetic studies of the oxide product 2 (obtained by the controlled heating of 1) indicate the presence of the Sr6Co5O15, detected by the diffraction method. Also, trace amounts of SrCoO2.75 and SrCoO2.5 were revealed by magnetic and DSC methods, respectively.

T1 Anisotropy Elucidates Spin Relaxation Mechanisms in an S = 1 Cr(IV) Optically Addressable Molecular Qubit.

Paramagnetic molecules offer unique advantages for quantum information science owing to their spatial compactness, synthetic tunability, room-temperature quantum coherence, and potential for optical state initialization and readout. However, current optically addressable molecular qubits are hampered by rapid spin-lattice relaxation (T1) even at sub-liquid nitrogen temperatures. Here, we use temperature- and orientation-dependent pulsed electron paramagnetic resonance (EPR) to elucidate the negative sign of the ground state zero-field splitting (ZFS) and assign T1 anisotropy to specific types of motion in an optically addressable S = 1 Cr(o-tolyl)4 molecular qubit. The anisotropy displays a distinct sin2(2θ) functional form that is not observed in S = 1/2 Cu(acac)2 or other Cu(II)/V(IV) microwave addressable molecular qubits. The Cr(o-tolyl)4 T1 anisotropy is ascribed to couplings between electron spins and rotational motion in low-energy acoustic or pseudoacoustic phonons. Our findings suggest that rotational degrees of freedom should be suppressed to maximize the coherence temperature of optically addressable qubits.

Spectroscopic and Computational Investigation of Low-Spin Mn(III) Bis(scorpionate) Complexes.

Six-coordinate MnIII complexes are typically high-spin (S = 2), however, the scorpionate ligand, both in its traditional, hydridotris(pyrazolyl)borate form, Tp- and Tp*- (the latter with 3,5-dimethylpyrazole substituents) and in an aryltris(carbene)borate (i.e., N-heterocyclic carbene, NHC) form, [Ph(MeIm)3B]-, (MeIm = 3-methylimidazole) lead to formation of bis(scorpionate) complexes of MnIII with spin triplet ground states; three of which were investigated herein: [Tp2Mn]SbF6 (1SBF6), [Tp*2Mn]SbF6 (2SBF6), and [{Ph(MeIm)3B}2Mn]CF3SO3 (3CF3SO3). These trigonally symmetric complexes were studied experimentally by magnetic circular dichroism (MCD) spectroscopy (the propensity of 3 to oxidize to MnIV precluded collection of useful MCD data) including variable temperatures and fields (VTVH-MCD) and computationally by ab initio CASSCF/NEVPT2 methods. These combined experimental and theoretical techniques establish the 3A2g electronic ground state for the three complexes, and provide information on the energy of the "conventional" high-spin excited state (5Eg) and other, triplet excited states. These results show the electronic effect of pyrazole ring substituents in comparing 1 and 2. The tunability of the scorpionate ligand, even by perhaps the simplest change (from pyrazole in 1 to 3,5-dimethylpyrazole in 2) is quantitatively manifested through perturbations in ligand-field excited-state energies that impact ground-state zero-field splittings. The comparison with the NHC donor is much more dramatic. In 3, the stronger σ-donor properties of the NHC lead to a quantitatively different electronic structure, so that the lowest lying spin triplet excited state, 3Eg, is much closer in energy to the ground state than in 1 or 2. The zero-field splitting (zfs) parameters of the three complexes were calculated and in the case of 1 and 2 compare closely to experiment (lower by < 10%, < 2 cm-1 in absolute terms); for 3 the large magnitude zfs is reproduced, although there is ambiguity about its sign. The comprehensive picture obtained for these bis(scorpionate) MnIII complexes provides quantitative insight into the role played by the scorpionate ligand in stabilizing unusual electronic structures.

Electromagnetically Induced Transparency in a Diamond Spin Ensemble Enables All-Optical Electromagnetic Field Sensing

We use electromagnetically induced transparency (EIT) to probe the narrow electron-spin resonance of nitrogen-vacancy centers in diamond. Working with a multipass diamond chip at temperatures 6-30 K, the zero-phonon absorption line (637 nm) exhibits an optical depth of 6 and inhomogeneous linewidth of ~30 GHz FWHM. Simultaneous optical excitation at two frequencies separated by the ground-state zero-field splitting (2.88 GHz) reveals EIT resonances with a contrast exceeding 6% and FWHM down to 0.4 MHz. The resonances provide an all-optical probe of external electric and magnetic fields with a projected photon-shot-noise-limited sensitivity of 0.2 V/cm/√[Hz] and 0.1 nT/√[Hz], respectively. Operation of a prototype diamond-EIT magnetometer measures a noise floor of ~/<1 nT/√[Hz] for frequencies above 10 Hz and Allan deviation of 1.3±1.1 nT for 100 s intervals. The results demonstrate the potential of diamond-EIT devices for applications ranging from quantum-optical memory to precision measurement and tests of fundamental physics.

Steric and Electronic Influences on the Structures of Peroxomanganese(III) Complexes Supported by Tetradentate Ligands

AbstractWe report the generation and characterization of two peroxomanganese(III) complexes supported by the L7py24‐Cl and L7iso‐q2 ligands {L7py24‐Cl = 1,4‐bis[(4‐chloro‐2‐pyridyl)methyl]‐1,4‐diazepane and L7iso‐q2 = 1,4‐bis[(2‐isoquinolinyl)methyl]‐1,4‐diazepane} and describe X‐ray structures of corresponding manganese(II) compounds. Ground and excited state properties of these peroxomanganese(III) complexes, as well as previously reported [MnIII(O2)(L7py24‐Me)]+ and [MnIII(O2)(L7q2)]+ species {L7py24‐Me = 1,4‐bis[(4‐methyl‐2‐pyridyl)methyl]‐1,4‐diazepane and L7q2 = 1,4‐bis[(2‐quinolinyl)methyl]‐1,4‐diazepane} were probed using low‐temperature electronic absorption, magnetic circular dichroism (MCD), and variable‐temperature, variable‐field MCD spectroscopy. These data sets afford electronic transition energies and estimates of ground‐state zero‐field splitting parameters, which permit a detailed comparison of electronic structure. These data support the proposal that all complexes share a similar geometry, consisting of a side‐on peroxomanganese(III) moiety coordinated by the tetradentate ligand in a trans fashion. However, differences in d‐d transition energies offer conclusive evidence that, among this series of complexes, it is the location, and thus the steric influence, of the pyridine substituent that modulates the electronic and geometric structure of the MnIII‐O2 unit. Within this series, perturbations in electronic properties of the supporting ligand have little impact on d‐d transition energies. Models of peroxomanganese(III) complexes developed using density functional theory (DFT) computations support this proposal, and time‐dependent DFT computations qualitatively reproduce the experimental trend in d‐d transition energies.

Geometric and Electronic Structures of Peroxomanganese(III) Complexes Supported by Pentadentate Amino-Pyridine and -Imidazole Ligands

Three peroxomanganese(III) complexes [Mn(III)(O(2))(mL(5)(2))](+), [Mn(III)(O(2))(imL(5)(2))](+), and [Mn(III)(O(2))(N4py)](+) supported by pentadentate ligands (mL(5)(2) = N-methyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine, imL(5)(2) = N-methyl-N,N',N'-tris((1-methyl-4-imidazolyl)methyl)ethane-1,2-diamine, and N4py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) were generated by treating Mn(II) precursors with H(2)O(2) or KO(2). Electronic absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD data demonstrate that these complexes have very similar electronic transition energies and ground-state zero-field splitting parameters, indicative of nearly identical coordination geometries. Because of uncertainty in peroxo (side-on η(2) versus end-on η(1)) and ligand (pentadentate versus tetradentate) binding modes, density functional theory (DFT) computations were used to distinguish between three possible structures: pentadentate ligand binding with (i) a side-on peroxo and (ii) an end-on peroxo, and (iii) tetradentate ligand binding with a side-on peroxo. Regardless of the supporting ligand, isomers with a side-on peroxo and the supporting ligand bound in a tetradentate fashion were identified as most stable by >20 kcal/mol. Spectroscopic parameters computed by time-dependent (TD) DFT and multireference SORCI methods provided validation of these isomers on the basis of experimental data. Hexacoordination is thus strongly preferred for peroxomanganese(III) adducts, and dissociation of a pyridine (mL(5)(2) and N4py) or imidazole (imL(5)(2)) arm is thermodynamically favored. In contrast, DFT computations for models of [Fe(III)(O(2))(mL(5)(2))](+) demonstrate that pyridine dissociation is not favorable; instead a seven-coordinate ferric center is preferred. These different results are attributed to the electronic configurations of the metal centers (high spin d(5) and d(4) for Fe(III) and Mn(III), respectively), which results in population of a metal-peroxo σ-antibonding molecular orbital and, consequently, longer M-O(peroxo) bonds for peroxoiron(III) species.

A Series of Peroxomanganese(III) Complexes Supported by Tetradentate Aminopyridyl Ligands: Detailed Spectroscopic and Computational Studies

A set of four [Mn(II)(L(7)py(2)(R))](2+) complexes, supported by the tetradentate 1,4-bis(2-pyridylmethyl)-1,4-diazepane ligand and derivatives with pyridine substituents in the 5 (R = Br) and 6 positions (R = Me and MeO), are reported. X-ray crystal structures of these complexes all show the L(7)py(2)(R) ligands bound to give a trans complex. Treatment of these Mn(II) precursors with either H(2)O(2)/Et(3)N or KO(2) in MeCN at -40 degrees C results in the formation of peroxomanganese complexes [Mn(III)(O(2))(L(7)py(2)(R))](+) differing only in the identity of the pyridine ring substituent. The electronic structures of two of these complexes, [Mn(III)(O(2))(L(7)py(2)(H))](+) and [Mn(III)(O(2))(L(7)py(2)(Me))](+), were examined in detail using electronic absorption, low-temperature magnetic circular dichroism (MCD) and variable-temperature variable-field (VTVH) MCD spectroscopies to determine ground-state zero-field splitting (ZFS) parameters and electronic transition energies, intensities, and polarizations. DFT and TD-DFT computations were used to validate the structures of [Mn(III)(O(2))(L(7)py(2)(H))](+) and [Mn(III)(O(2))(L(7)py(2)(Me))](+), further corroborating their assignment as peroxomanganese(III) species. While these complexes exhibit similar ZFS parameters, their low-temperature MCD spectra reveal significant shifts in electronic transition energies that are correlated to differences in Mn-O(2) interactions among these complexes. Taken together, these results indicate that, while the [Mn(III)(O(2))(L(7)py(2)(H))](+) complex exhibits symmetric Mn-O(peroxo) bond lengths, consistent with a side-on bound peroxo ligand, the peroxo ligand of the [Mn(III)(O(2))(L(7)py(2)(Me))](+) complex is bound in a more end-on fashion, with asymmetric Mn-O(peroxo) distances. This difference in binding mode is rationalized in terms of the greater electron-donating abilities of the methyl-appended pyridines and suggests a simple way to modulate Mn(III)-O(2) bonding through ligand perturbations.

A model for spectral diffusion induced by resonant energy migration applied to the 4A 2→ 2E transition of Cr 3+ in [Cr(ox) 3] 3− (ox=C 2O 42−)

In the 3D oxalate networks [NaCr(ox) 3][Rh(bpy) 3]ClO 4 and [NaCr(ox) 3][Ru(bpy) 3] (ox=oxalate, bpy=2,2′-bipyridine) three different types of energy migration within the 4A 2→ 2E transition can be identified. One is a resonant process between spectral members spaced by the ground-state zero-field splitting (ZFS). This leads to the sequential appearance of additional sharp lines spaced by the ground-state ZFS in the fluorescence line narrowing spectrum across the inhomogeneous line. The second one is a quasi-resonant process between spectral neighbours and manifests itself by rapid spectral diffusion. The third one is the well-known phonon-assisted process setting in at higher temperature.

Magnetic circular dichroism spectroscopy of antiferromagnetically coupled hetero-metallic rings [H2NR2][Cr7MF8(O2CCMe3)16

The optical and magnetic properties of the multi-metal rings [NH(2)R(2)][Cr(7)MF(8)(O(2)CCMe(3))(16)], where M = Cd(II), Mn(II) or Ni(II), have been studied using variable-field and variable-temperature magnetic circular dichroism (MCD) in the UV-visible spectra. Spectra of samples were recorded in a frozen organic matrix or cast in a polymethacrylate (PMMA) polymer film between 1.7 and 75 K. The spectra are characteristic of the Cr(III) ion (d(3)) in a rhombic field when M = Cd(II). In the case that M = Ni(II) additional optical transitions arise from the d(8) ion whereas for M = Mn(II) no additional transitions are observed. The influence of magnetic exchange is apparent from a change in the sign of the MCD signal between complexes in which the hetero-atom has a local spin moment greater, or less, than that of Cr(III), S = 3/2, namely, Mn(II), S = 5/2, and Ni(II), S = 1. The exchange coupling generates a manifold of thermally accessible electronic states that give rise to variations in MCD intensity as well as additional spectral features as the temperature is raised. Equations have been derived to relate the splittings observed in the optical spectrum to the single-ion ground state zero-field splittings of chromium(III). There is reasonable agreement between the sign and magnitude of the contribution to the cluster anisotropy from that of the single ion with values estimated from other techniques.

Theoretical investigations of zero-field splitting of excited states for 3d 3 ions in trigonal crystal fields

By taking into account slight interactions, i.e. spin–spin, spin–other-orbit and orbit–orbit interactions, in addition to spin–orbit interaction, the zero-field splitting of ground state and low excited states and g factors of ZnGa 2O 4:Cr 3+ crystal have been interpreted systematically. And the contributions to zero-field splitting arising from slight magnetic interaction and trigonal crystal field are investigated. It is found that there exist combined mechanism between magnetic interactions and trigonal crystal field.

Theoretical study of anisotropy spin-orbit coupling and local lattice structure for Fe3+ ions in MgTiO3:Fe3+ system

The anisotropy spin-orbit coupling matrices for a d5 configuration ion in a trigonal ligand-field have been established. On basis of the anisotropy spin-orbit coupling matrices, the ground state zero-field splitting of the Fe3+ ions in ilmenite-structure MgTiO3:Fe3+ system has been studied. The calculated results show that the anisotropy of Fe3+ ions in the diamagnetic ilmenite MgTiO3 is important and the EPR parameters depend sensitively on the anisotropy divergent parameter. Moreover, the effect of the anisotropy divergent parameter on the second-order parameter D is obviously larger than that on the fourth-order parameter (a-F). Based on this point, the local lattice structure of Fe3+ ion in MgTiO3:Fe3+ system is determined by diagonalizing the complete energy matrices for a d5 configuration ion in a trigonal ligand-field and considering the second-order as well as the fourth-order EPR parameters D and (a-F) simultaneously. Our results are consistent with the experimental proposal that Fe3+ ions may locate at both the Mg2+ and Ti4+ sites.

Energy Spectrum of YAG:Cr3+ and Thermal Shifts of Its R Lines

Traditional ligand-field theory has to be improved by taking into accountboth ``pure electronic'' contribution and electron-phonon interaction one(including lattice-vibrational relaxation energy). By means of improvedligand-field theory, R1, R2, R'3, R'2, and R'1lines, U band, ground-state zero-field-splitting (GSZFS) and ground-state gfactors as well as thermal shifts of R1 line and R2 line ofYAG:Cr3+ have been calculated. The results are in very good agreementwith the experimental data. In contrast with ruby, the octahedron of ligandoxygen ions surrounding the central Cr3+ ion in YAG:Cr3+ iscompressed along the [111] direction. Thus, for YAG:Cr3+ and ruby,the splitting of t23 4A2 (or t23 2E) has opposite order,and the trigonal-field parameters of the two crystals have opposite signs.In thermal shifts of R1 and R2 lines of YAG:Cr3+, thetemperature-dependent contributions due to EPI are dominant.

Improved Ligand-Field Theory with Effect of Electron-Phonon Interaction

Traditional ligand-field theory has to be improved by taking into accountboth ``pure electronic'' contribution and electron-phonon interaction one(including lattice-vibrational relaxation energy). By means of improvedligand-field theory, R1, R2, R′3, R′2, and R′1lines, U band, ground-state zero-field-splitting (GSZFS), and ground-state g factorsof ruby and/or GSGG: Cr3+ as well as thermal shifts of GSZFS, R1 line and R2 line of ruby have been calculated. The results arein very good agreement with the experimental data. Moreover, it is foundthat the value of cubic-field parameter given by traditional ligand-fieldtheory is inappropriately large. For thermal shifts of GSZFS, R1 lineand R2 line of ruby, several conclusions have also been obtained.

A covalent model of the optical spectra and EPR parameters for CdS:Ti2+

AbstractIn this paper, formulas for the optical spectrum and the EPR parameters calculated for d2 ions in Td symmetry are established by using a covalent model, in which the covalence contribution has been considered. Using the model, we have calculated the optical spectra and the ground‐state gyromagnetic factor and zero‐field splitting of CdS:Ti2+. The calculated results could explain well the experimental findings. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Analysis of ground-state zero-field splitting for Mn 2+ in hexagonal ZnS:Mn 2+

The ground state splitting of d 5 configuration ion Mn 2+ in ZnS:Mn 2+ has been studied by diagonalizing the energy matrices for electron–electron repulsion, spin–orbit coupling and trigonal ligand field interactions. It is shown that in order to give a unified explanation for the EPR parameters a, D and ( a− F) for Mn 2+ in ZnS:Mn 2+, a positive Dq has to be employed. This means that in tetrahedral ZnS the sulfur ion has a positive effective charge. This unusual result supports the Pauling's speculation that the sulfur ion in ZnS may be looked upon as an electron donor that forms a quadricovalent argon state of S 2+ with sp 3 hybrid configuration.

Theoretical Calculations of Thermal Shifts of Ground-State Zero-Field-Splitting for Ruby

By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of wavefunctions within electronic configuration, the thermal shifts (TS) of the ground-state zero-field-splitting (GSZFS) due to EPI for ruby have microscopic-theoretically been calculated; the contribution to TS of GSZFS from thermal expansion has also been calculated. The results are in very good agreement with experiments. It is found that the contributions from the first-order perturbation of the second-order term in EPI Hamiltonian are dominant in the Raman term and optical-branch term for TS of GSZFS; the different between the TS due to EPI of level and the TS due to EPI of level gives rise to the TS due to EPI of GSZFS, which is very small in comparison with the TS due to EPI of or level. Among various terms in TS of GSZFS, Raman term is the largest one and the signs of the Raman term and optical-branch term are opposite to the sign of the thermal-expansion term; the optical-branch term plays an important role in TS of GSZFS and increases rapidly with temperature; all various contributions to TS of GSZFS have to be taken into account, since the subtle balance among them determines the total result. The comparison between the features of TS of GSZFS and those of TS of and lines has been made. For TS of GSZFS, the contribution from thermal expansion is especially important; the neighbor-level term is insignificant.

Energy Spectrum and Its Pressure-Induced Shift and g Factor of ZnS:Mn2+

By using strong-field scheme, the complete d5 energy matrix with D2d symmetry has been constructed. Then, by diagonalization of this matrix at normal and various pressures,the whole energy spectrum [including the ground-state zero-field-splitting (GSZFS)], its PS and the g factor of the ground state for ZnS:Mn2+ have uniformly been calculated. According to the eigenfunctions and PS, the new assignments of five absorption bands have been given.The variation of tetragonal field with pressure makes a main contribution to the pressureinduced shift (PS) of GSZFS of ZnS:Mn2+, which supports the existence of tetragonal Jahn-Teller distortion in ZnS:Mn2+. It is found that when P≥62 kbar, merges with , which has to be taken into account in the calculation of PS of the fifth band in the range of 1 bar ~95 kbar. It is demonstrated that the Mn2+ ions in ZnS:Mn2+ have tetrahedral coordination, and the difference between ζ and ζ′ caused by the covalency effect is very important for GSZFS. The physical essentials of typical levels, GSZFS and their PS have been revealed. By taking into account the influence of covalency on and , the positon of the third absorption band at normal pressure has been estimated.

Energy Spectrum and Its Pressure-Induced Shift and J-T Effect of ZnTe:Mn2+

By using strong-field scheme, the complete d5 energy matrix with D2d symmetry has been constructed. Then, by diagonalization of this matrix at normal and various pressures,the whole energy spectrum [including the ground-state zero-field splitting (GSZFS)] and its pressure-induced shift (PS) of ZnTe:Mn2+ have uniformly been calculated. The results are in very good agreement with experimental data. According to the eigenfimctions and PS, the assignments of four absorption bands have been given. By taking into account the dect of different deformations of t2 and e radial wavefunctions on and , the position of the third absorption band at normal pressure has been estimated.The tetragonal field is important for GSZFS of ZnTe:Mn2+ and its PS, which supports the existence of tetragonal Jahn-Teller distortion in ZnTe:Mn2+ The physical essentials of typical levels, GSZFS and their PS have been revealed.