Showing papers on "Spin states published in 2013"
TL;DR: The article deals with coordination compounds of iron(II) that may exhibit thermally induced spin transition, known as spin crossover, depending on the nature of the coordinating ligand sphere, and the variety of physical techniques usually applied for their characterization.
Abstract: The article deals with coordination compounds of iron(II) that may exhibit thermally induced spin transition, known as spin crossover, depending on the nature of the coordinating ligand sphere. Spin transition in such compounds also occurs under pressure and irradiation with light. The spin states involved have different magnetic and optical properties suitable for their detection and characterization. Spin crossover compounds, though known for more than eight decades, have become most attractive in recent years and are extensively studied by chemists and physicists. The switching properties make such materials potential candidates for practical applications in thermal and pressure sensors as well as optical devices. The article begins with a brief description of the principle of molecular spin state switching using simple concepts of ligand field theory. Conditions to be fulfilled in order to observe spin crossover will be explained and general remarks regarding the chemical nature that is important for the occurrence of spin crossover will be made. A subsequent section describes the molecular consequences of spin crossover and the variety of physical techniques usually applied for their characterization. The effects of light irradiation (LIESST) and application of pressure are subjects of two separate sections. The major part of this account concentrates on selected spin crossover compounds of iron(II), with particular emphasis on the chemical and physical influences on the spin crossover behavior. The vast variety of compounds exhibiting this fascinating switching phenomenon encompasses mono-, oligoand polynuclear iron(II) complexes and cages, polymeric 1D, 2D and 3D systems, nanomaterials, and polyfunctional materials that combine spin crossover with another physical or chemical property.
586 citations
TL;DR: It is demonstrated, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters.
Abstract: In spin-based electronics, information is encoded by the spin state of electron bunches Processing this information requires the controlled transport of spin angular momentum through a solid, preferably at frequencies reaching the so far unexplored terahertz regime Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures A laser pulse is used to drive spins from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter based on the inverse spin Hall effect, which converts the spin flow into a terahertz electromagnetic pulse We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters
485 citations
TL;DR: The findings suggest the use of chemically amenable phenalenyl-based molecules as a viable and scalable platform for building molecular-scale quantum spin memory and processors for technological development.
Abstract: When molecules of a phenalenyl derivative, which has no net spin, are deposited on a ferromagnet, they develop into a magnetic supramolecular layer with spin-filtering properties; this could be the basis for a new approach to building molecular magnetic devices. Various types of molecular magnets carrying high localized spin have been studied as potential devices for information processing and storage, but it remains a considerable challenge to electronically couple to these spin centres. Moodera et al. have designed a phenalenyl derivative, essentially a graphene fragment, with the potential to act as an interface for the exchange of magnetic spin information in molecular spintronic devices. The graphene fragment has no net spin itself, but when deposited as a layer on a ferromagnet it transforms to produce a supramolecular magnetic film. The resulting nanoscale magnetic molecules, or memory 'bits', can be manipulated by external stimuli, and the resulting device exhibits an unexpectedly large magnetoresistance of 20% near room temperature. The use of molecular spin state as a quantum of information for storage, sensing and computing has generated considerable interest in the context of next-generation data storage and communication devices1,2, opening avenues for developing multifunctional molecular spintronics3. Such ideas have been researched extensively, using single-molecule magnets4,5 and molecules with a metal ion6 or nitrogen vacancy7 as localized spin-carrying centres for storage and for realizing logic operations8. However, the electronic coupling between the spin centres of these molecules is rather weak, which makes construction of quantum memory registers a challenging task9. In this regard, delocalized carbon-based radical species with unpaired spin, such as phenalenyl10, have shown promise. These phenalenyl moieties, which can be regarded as graphene fragments, are formed by the fusion of three benzene rings and belong to the class of open-shell systems. The spin structure of these molecules responds to external stimuli11,12 (such as light, and electric and magnetic fields), which provides novel schemes for performing spin memory and logic operations. Here we construct a molecular device using such molecules as templates to engineer interfacial spin transfer resulting from hybridization and magnetic exchange interaction with the surface of a ferromagnet; the device shows an unexpected interfacial magnetoresistance of more than 20 per cent near room temperature. Moreover, we successfully demonstrate the formation of a nanoscale magnetic molecule with a well-defined magnetic hysteresis on ferromagnetic surfaces. Owing to strong magnetic coupling with the ferromagnet, such independent switching of an adsorbed magnetic molecule has been unsuccessful with single-molecule magnets13. Our findings suggest the use of chemically amenable phenalenyl-based molecules as a viable and scalable platform for building molecular-scale quantum spin memory and processors for technological development.
373 citations
TL;DR: It is shown that the 4H, 6H and 3C polytypes of SiC all host coherent and optically addressable defect spin states, including states in all three with room-temperature quantum coherence, which shows that crystal polymorphism can be a degree of freedom for engineering spin qubits.
Abstract: Crystal defects can confine isolated electronic spins and are promising candidates for solid-state quantum information. Alongside research focusing on nitrogen-vacancy centres in diamond, an alternative strategy seeks to identify new spin systems with an expanded set of technological capabilities, a materials-driven approach that could ultimately lead to 'designer' spins with tailored properties. Here we show that the 4H, 6H and 3C polytypes of SiC all host coherent and optically addressable defect spin states, including states in all three with room-temperature quantum coherence. The prevalence of this spin coherence shows that crystal polymorphism can be a degree of freedom for engineering spin qubits. Long spin coherence times allow us to use double electron-electron resonance to measure magnetic dipole interactions between spin ensembles in inequivalent lattice sites of the same crystal. Together with the distinct optical and spin transition energies of such inequivalent states, these interactions provide a route to dipole-coupled networks of separately addressable spins.
308 citations
TL;DR: A novel restricted-open-shell configuration interaction with singles (ROCIS) approach for the calculation of transition metal L-edge X-ray absorption spectra is introduced and it is advantageous to employ Kohn-Sham rather than Hartree-Fock orbitals thus defining the density functional theory∕R OCIS method.
Abstract: A novel restricted-open-shell configuration interaction with singles (ROCIS) approach for the calculation of transition metal L-edge X-ray absorption spectra is introduced. In this method, one first calculates the ground state and a number of excited states of the non-relativistic Hamiltonian. By construction, the total spin is a good quantum number in each of these states. For a ground state with total spin S excited states with spin S′ = S, S − 1, and S + 1 are constructed. Using Wigner-Eckart algebra, all magnetic sublevels with MS = S, …, −S for each multiplet of spin S are obtained. The spin-orbit operator is represented by a mean-field approximation to the full Breit-Pauli spin-orbit operator and is diagonalized over this N-particle basis. This is equivalent to a quasi-degenerate treatment of the spin-orbit interaction to all orders. Importantly, the excitation space spans all of the molecular multiplets that arise from the atomic Russell-Saunders terms. Hence, the method represents a rigorous first-principles approach to the complicated low-symmetry molecular multiplet problem met in L-edge X-ray absorption spectroscopy. In order to gain computational efficiency, as well as additional accuracy, the excitation space is restricted to single excitations and the configuration interaction matrix is slightly parameterized in order to account for dynamic correlation effects in an average way. To this end, it is advantageous to employ Kohn-Sham rather than Hartree-Fock orbitals thus defining the density functional theory/ROCIS method. However, the method can also be used in an entirely non-empirical fashion. Only three global empirical parameters are introduced and have been determined here for future application of the method to any system containing any transition metal. The three parameters were carefully calibrated using the L-edge X-ray absorption spectroscopy spectra of a test set of coordination complexes containing first row transition metals. These parameters are universal and transferable. Hence, there are no adjustable parameters that are used to fit experimental X-ray absorption spectra. Thus, the new approach classifies as a predictive first-principles method rather than an analysis tool. A series of calculations on transition metal compounds containing Cu, Ti, Fe, and Ni in various oxidation and spin states is investigated and a detailed comparison to experimental data is reported. In most cases, the approach yields good to excellent agreement with experiment. In addition, the origin of the observed spectral features is discussed in terms of the electronic structure of the investigated compounds.
207 citations
TL;DR: In this paper, a systematic study of soft X-ray absorption spectroscopy in various manganese oxides and fluorides was performed and compared with each other, showing that the Mn-L spectra fingerprint the Mn valence and spin states through spectral lineshape and energy position consistently and evidently.
160 citations
TL;DR: In this article, the role of phase coherence between the two spin components and the magnitude of the spin-polarization vector, rather than its orientation in spin space, was investigated for supercurrent stability.
Abstract: We create and study persistent currents in a toroidal two-component Bose gas, consisting of 87Rb atoms in two different spin states. For a large spin-population imbalance we observe supercurrents persisting for over two minutes. However, we find that the supercurrent is unstable for spin polarization below a well-defined critical value. We also investigate the role of phase coherence between the two spin components and show that only the magnitude of the spin-polarization vector, rather than its orientation in spin space, is relevant for supercurrent stability.
155 citations
TL;DR: The Ce electronic structure is monitored during the synthesis and catalase mimetic reaction of colloidal ceria nanoparticles under in situ conditions by means of high-energy resolution hard X-ray spectroscopy and confirms strong orbital mixing between Ce and O, and the Ce spin state is conserved during the reaction.
Abstract: The catalytic performance of ceria nanoparticles is generally attributed to active sites on the particle surface. The creation of oxygen vacancies and thus nonstoichiometric CeO2−δ has been proposed to result in Ce3+ sites with unpaired f electrons which can be oxidized to spinless Ce4+ ions during catalytic reactions. We monitored the Ce electronic structure during the synthesis and catalase mimetic reaction of colloidal ceria nanoparticles under in situ conditions. By means of high-energy resolution hard X-ray spectroscopy, we directly probed the Ce 4f and 5d orbitals. We observe pronounced changes of the Ce 5d bands upon reduction of the particle size and during the catalytic reaction. The Ce 4f orbitals, however, remain unchanged, and we do not observe any significant number of spin-unpaired Ce3+ sites even for catalytically active small (3 nm) particles with large surface to bulk ratio. This confirms strong orbital mixing between Ce and O, and the Ce spin state is conserved during the reaction. The p...
150 citations
TL;DR: In this paper, a long-lived quantum-dot spin qubit coupled to a GaAs-based photonic crystal cavity was used to control the charge state of the InAs quantum dot using laser pulses.
Abstract: Using a long-lived quantum-dot spin qubit coupled to a GaAs-based photonic crystal cavity, researchers demonstrate complete quantum control of an electron spin qubit. By cleverly controlling the charge state of the InAs quantum dot using laser pulses, optical initialization, control and readout of an electron spin are achieved.
150 citations
TL;DR: In this paper, the authors investigated the O2 dissociation after the chemisorption on the metal center of M-N4 moieties in graphene and found that the minimum energy paths and saddle points for the oxygen reduction reaction (ORR) in allowed spin states have been identified.
Abstract: The O2 dissociation after the chemisorption on the metal center of M–N4 moieties in graphene (with M = Mn, Fe, and Co) is addressed by density functional theory calculations. Both minimum energy paths and saddle points for the oxygen reduction reaction (ORR) in the allowed spin states have been identified. Our calculations indicate that ORR can evolve through different spin states, those where the M–O2 adducts are stable. We find that Mn–N4 and Fe–N4 centers in graphene exhibit the lowest O2 dissociation energies of ∼0.7 and 1.1 eV, respectively, over three spin channels, while for Co–N4 we find two spin channels with the same dissociation energy of ∼1.6 eV. The O2 dissociation barriers on the Mn–N4 and Fe–N4 centers are comparable to that found on Pt(111), suggesting similar ORR catalytic activity, in agreement with experimental results.
148 citations
TL;DR: The results clearly demonstrate that temperature- and light-induced spin crossover is possible for isolated molecules on surfaces but that interactions with the surface may play a key role in determining when this can occur.
Abstract: Using X-ray absorption techniques, we show that temperature- and light-induced spin crossover properties are conserved for a submonolayer of the [Fe(H2B(pz)2)2(2,2′-bipy)] complex evaporated onto a Au(111) surface. For a significant fraction of the molecules, we see changes in the absorption at the L2,3 edges that are consistent with those observed in bulk and thick film references. Assignment of these changes to spin crossover is further supported by multiplet calculations to simulate the X-ray absorption spectra. As others have observed in experiments on monolayer coverages, we find that many molecules in our submonolayer system remain pinned in one of the two spin states. Our results clearly demonstrate that temperature- and light-induced spin crossover is possible for isolated molecules on surfaces but that interactions with the surface may play a key role in determining when this can occur.
TL;DR: The nature and magnitude of the magnetic anisotropy of heptacoordinate mononuclear Ni( II) and Co(II) complexes were investigated by a combination of experiment and ab initio calculations to rationalize the magnitude and the sign of D.
Abstract: The nature and magnitude of the magnetic anisotropy of heptacoordinate mononuclear Ni(II) and Co(II) complexes were investigated by a combination of experiment and ab initio calculations. The zero-field splitting (ZFS) parameters D of [Ni(H(2)DAPBH)(H(2)O)(2)](NO(3))(2)⋅2 H(2)O (1) and [Co(H(2)DAPBH)(H(2)O)(NO(3))](NO(3)) [2; H(2)DAPBH = 2,6-diacetylpyridine bis- (benzoyl hydrazone)] were determined by means of magnetization measurements and high-field high-frequency EPR spectroscopy. The negative D value, and hence an easy axis of magnetization, found for the Ni(II) complex indicates stabilization of the highest M(S) value of the S = 1 ground spin state, while a large and positive D value, and hence an easy plane of magnetization, found for Co(II) indicates stabilization of the M(S) = ±1/2 sublevels of the S = 3/2 spin state. Ab initio calculations were performed to rationalize the magnitude and the sign of D, by elucidating the chemical parameters that govern the magnitude of the anisotropy in these complexes. The negative D value for the Ni(II) complex is due largely to a first excited triplet state that is close in energy to the ground state. This relatively small energy gap between the ground and the first excited state is the result of a small energy difference between the d(xy) and d(x(2)-y(2)) orbitals owing to the pseudo-pentagonal-bipyramidal symmetry of the complex. For Co(II), all of the excited states contribute to a positive D value, which accounts for the large magnitude of the anisotropy for this complex.
TL;DR: The theoretical study shows that, for an ideally trigonal Ni(II) complex, the orbital degeneracy leads to a first-order spin-orbit coupling that results in a splitting of the M(s) = ± 1 and M(S) = 0 components of the ground spin state of approximately -600 cm(-1).
Abstract: This paper reports the experimental and theoretical investigations of two trigonal bipyramidal Ni(II) complexes, [Ni(Me6tren)Cl](ClO4) (1) and [Ni(Me6tren)Br](Br) (2). High-field, high-frequency electron paramagnetic resonance spectroscopy performed on a single crystal of 1 shows a giant uniaxial magnetic anisotropy with an experimental Dexpt value (energy difference between the Ms = ± 1 and Ms = 0 components of the ground spin state S = 1) estimated to be between −120 and −180 cm–1. The theoretical study shows that, for an ideally trigonal Ni(II) complex, the orbital degeneracy leads to a first-order spin–orbit coupling that results in a splitting of the Ms = ± 1 and Ms = 0 components of approximately −600 cm–1. Despite the Jahn–Teller distortion that removes the ground term degeneracy and reduces the effects of the first-order spin–orbit interaction, the D value remains very large. A good agreement between theoretical and experimental results (theoretical Dtheor between −100 and −200 cm–1) is obtained.
TL;DR: When a paramagnetic molecule is placed on a superconducting surface the lifetime of its spin excitations increases dramatically as discussed by the authors, caused by the depletion of the electronic states within the energy gap at the Fermi level.
Abstract: When a paramagnetic molecule is placed on a superconducting surface the lifetime of its spin excitations increases dramatically. This effect, caused by the depletion of the electronic states within the energy gap at the Fermi level, could find application in coherent spin manipulation.
TL;DR: In this paper, the analysis of 2p XAS, XMCD and 2p EELS is discussed, including isolated iron atoms, solids and coordination compounds, including binary oxides, perovskites and spinel systems.
TL;DR: In this article, the authors demonstrate that the Kondo resonance of manganese phthalocyanine molecules on a Au(111) substrate can be switched off and on via attachment and detachment of a single hydrogen atom to the magnetic core of the molecule.
Abstract: The reversible control of a single spin of an atom or a molecule is of great interest in Kondo physics and a potential application in spin based electronics. Here we demonstrate that the Kondo resonance of manganese phthalocyanine molecules on a Au(111) substrate have been reversibly switched off and on via a robust route through attachment and detachment of single hydrogen atom to the magnetic core of the molecule. As further revealed by density functional theory calculations, even though the total number of electrons of the Mn ion remains almost the same in the process, gaining one single hydrogen atom leads to redistribution of charges within 3d orbitals with a reduction of the molecular spin state from S = 3/2 to S = 1 that directly contributes to the Kondo resonance disappearance. This process is reversed by a local voltage pulse or thermal annealing to desorb the hydrogen atom.
TL;DR: A specific antidot structure, the only S-terminated antidot, was determined to exhibit a large net spin with long-range ferromagnetic coupling above room temperature, suitable for experimental verification and implementation opening a new path to explore MoS2-based magnetic nanostructures.
Abstract: Developing approaches to effectively induce and control the magnetic states is critical to the use of magnetic nanostructures in quantum information devices but is still challenging. Here MoS2-based nanostructures including atomic defects, nanoholes, nanodots and antidots are characterized with spin-polarized density functional theory. The S-vacancy defect is more likely to form than the Mo-vacancy defect due to the form of Mo–Mo metallic bonds. Among different shaped nanoholes and nanodots, triangle ones associated with ferromagnetic characteristic are most energetically favorable, and exhibit unexpected large spin moments that scale linearly with edged length. In particular, S-terminated triangle nanodots show strong spin anisotropy around the Fermi level with a substantial collective characteristic of spin states at edges, enabling it to a desired spin-filtering structure. However, in the antidot, the net spin, coupled order and stability of spin states can be engineered by controlling type and distance of internal nanoholes. Based on the analysis of the spin coupled mechanism, a specific antidot structure, the only S-terminated antidot, was determined to exhibit a large net spin with long-range ferromagnetic coupling above room temperature. Given the recent achievement of graphene- and BN-based nanohole, nanodot and antidot structures, we believe that our calculated results are suitable for experimental verification and implementation opening a new path to explore MoS2-based magnetic nanostructures.
TL;DR: Because of the outstanding photophysical properties of diarylethenes, including single-crystalline photochromism, molecular switch 1 may offer a promising platform for controlling the magnetic properties in the solid state and ultimately at the single-molecule level with light at room temperature.
Abstract: A photoisomerizable diarylethene-derived ligand, phen*, has been successfully introduced into a spin-crossover iron(II) complex, [Fe(H2B(pz)2)2phen*] (1; pz =1-pyrazolyl). A ligand-based photocyclization (photocycloreversion) in 1 modifies the ligand field, which, in turn, results in a highly efficient paramagnetic high-spin → diamagnetic low-spin (low-spin → high-spin) transition at the coordinated Fe(II) ion. The reversible photoswitching of the spin states, and thus the associated magnetic properties, has been performed in solution at room temperature and has been directly monitored by measuring the magnetic susceptibility via the Evans method. The observed spin-state photoconversion in 1 exceeds 40%, which is the highest value for spin-crossover molecular switches in solution at room temperature reported to date. The photoexcited state is extraordinarily thermally stable, showing a half-time of about 18 days in solution at room temperature. Because of the outstanding photophysical properties of diarylethenes, including single-crystalline photochromism, molecular switch 1 may offer a promising platform for controlling the magnetic properties in the solid state and ultimately at the single-molecule level with light at room temperature.
TL;DR: The influence of cobalt and manganese coordination on the oxygen evolution reaction (OER) activity and oxide stability in alkaline solution was studied in this article, where high-resolution transmission electron microscopy (HRTEM) and X-ray absorption spectroscopy (XAS) were combined to confirm the presence of coordination environments such as Co2+ in disordered prisms and Co4+/Mn4+ in face shared octahedra.
Abstract: Several coordination motifs of cobalt and manganese ions were obtained in various transition metal oxides, which enabled different oxidation and spin states. Combined high-resolution transmission electron microscopy (HRTEM) and X-ray absorption spectroscopy (XAS) confirmed the presence of coordination environments such as Co2+ in disordered prisms and Co4+/Mn4+ in face-shared octahedra. The influence of cobalt and manganese coordination on the oxygen evolution reaction (OER) activity and oxide stability in alkaline solution was studied. Under cycling, the surface of perovskites that consists of Co2+ in prisms was amorphized and the activity was similar to that of LaCoO3, which has a stable surface composed of Co3+ in octahedral coordination. These findings highlight the critical role of the electronic structure of transition metal oxides on the OER activity and stability.
TL;DR: It is predicted that the stable 2D LaOBiS2 with only 1 nm of thickness can produce remarkable Rashba spin splitting with a magnitude of 100 meV, and an advanced Datta-Das SFET model is proposed that consists of dual gates and 2DLaOBi s2 channels by selecting different Rashba states to achieve the on-off switch via electric fields.
Abstract: Rashba spin splitting is a two-dimensional (2D) relativistic effect closely related to spintronics. However, so far there is no pristine 2D material to exhibit enough Rashba splitting for the fabrication of ultrathin spintronic devices, such as spin field effect transistors (SFET). On the basis of first-principles calculations, we predict that the stable 2D LaOBiS2 with only 1 nm of thickness can produce remarkable Rashba spin splitting with a magnitude of 100 meV. Because the medium La2O2 layer produces a strong polar field and acts as a blocking barrier, two counter-helical Rashba spin polarizations are localized at different BiS2 layers. The Rashba parameter can be effectively tuned by the intrinsic strain, while the bandgap and the helical direction of spin states sensitively depends on the external electric field. We propose an advanced Datta-Das SFET model that consists of dual gates and 2D LaOBiS2 channels by selecting different Rashba states to achieve the on–off switch via electric fields.
TL;DR: R'-substituents have little influence on the efficiency and chemoselectivity of the catalytic activity of the complexes, but the selectivity toward olefin cis-dihydroxylation is enhanced for complexes with R = Me, F, or Cl.
Abstract: A family of iron complexes with the general formula [FeII(R,R′Pytacn)(X)2]n+ is described, where R,R′Pytacn is the tetradentate ligand 1-[(4-R′-6-R-2-pyridyl)methyl]-4,7-dimethyl-1,4,7-triazacyclononane, R refers to the group at the α-position of the pyridine, R′ corresponds to the group at the γ-position, and X denotes CH3CN or CF3SO3. Herein, we study the influence of the pyridine substituents R and R′ on the electronic properties of the coordinated iron center by a combination of structural and spectroscopic characterization using X-ray diffraction, 1H NMR and UV–vis spectroscopies, and magnetic susceptibility measurements. The electronic properties of the substituent in the γ-position of the pyridine ring (R′) modulate the strength of the ligand field, as shown by magnetic susceptibility measurements in CD3CN solution, which provide a direct indication of the population of the magnetically active high-spin S = 2 ferrous state. Indeed, a series of complexes [FeII(H,R′Pytacn)(CD3CN)2]2+ exist as mixture...
TL;DR: The local density of states measured for different spin states shows that high- spin molecules have a smaller transport gap than low-spin molecules and are in agreement with density functional theory calculations.
Abstract: Scanning tunneling microscopy and local conductance mapping show spin-state coexistence in bilayer films of Fe[(H2Bpz2)2bpy] on Au(111) that is independent of temperature between 131 and 300 K. This modification of bulk behavior is attributed in part to the unique packing constraints of the bilayer film that promote deviations from bulk behavior. The local density of states measured for different spin states shows that high-spin molecules have a smaller transport gap than low-spin molecules and are in agreement with density functional theory calculations.
TL;DR: The results indicate that while DFT is well suited for the prediction of structural parameters, an accurate multiconfigurational approach is essential for the quantitative determination of ΔEHL, and a good qualitative agreement is found between the TD-DFT and CASPT2 potential energy curves.
Abstract: The electronic structure relevant to low spin (LS)↔high spin (HS) transitions in Fe(II) coordination compounds with a FeN6 core are studied. The selected [Fe(tz)6]2+ (1) (tz = 1H-tetrazole), [Fe(bipy)3]2+ (2) (bipy = 2,2′-bipyridine), and [Fe(terpy)2]2+ (3) (terpy = 2,2′:6′,2″-terpyridine) complexes have been actively studied experimentally, and with their respective mono-, bi-, and tridentate ligands, they constitute a comprehensive set for theoretical case studies. The methods in this work include density functional theory (DFT), time-dependent DFT (TD-DFT), and multiconfigurational second order perturbation theory (CASPT2). We determine the structural parameters as well as the energy splitting of the LS–HS states (ΔEHL) applying the above methods and comparing their performance. We also determine the potential energy curves representing the ground and low-energy excited singlet, triplet, and quintet d6 states along the mode(s) that connect the LS and HS states. The results indicate that while DFT is we...
TL;DR: In this paper, the magnetic field has no effect on the initial fluorescence decay rate but affects the decay after the triplet pair states begin to equilibrate with the singlets.
TL;DR: In this article, the authors demonstrate a scheme to couple bright NV electronic spins to dark substitutional-nitrogen (P1) electronic spins by dressing their spin states with oscillating magnetic fields.
Abstract: Under ambient conditions, spin impurities in solid-state systems are found in thermally mixed states and are optically ‘‘dark’’; i.e., the spin states cannot be optically controlled. Nitrogen-vacancy (NV) centers in diamond are an exception in that the electronic spin states are ‘‘bright’’; i.e., they can be polarized by optical pumping, coherently manipulated with spin-resonance techniques, and read out optically, all at room temperature. Here we demonstrate a scheme to resonantly couple bright NV electronic spins to dark substitutional-nitrogen (P1) electronic spins by dressing their spin states with oscillating magnetic fields. This resonant coupling mechanism can be used to transfer spin polarization from NV spins to nearby dark spins and could be used to cool a mesoscopic bath of dark spins to near-zero temperature, thus providing a resource for quantum information and sensing, and aiding studies of quantum effects in many-body spin systems.
TL;DR: The Mn(IV)3CaO4 cubane is a structural motif present in the oxygen-evolving complex (OEC) of photosystem II and in water-oxidizing Mn/Ca layered oxides and a series of idealized models that incorporate this structural unit are investigated.
Abstract: The Mn(IV)3CaO4 cubane is a structural motif present in the oxygen-evolving complex (OEC) of photosystem II and in water-oxidizing Mn/Ca layered oxides. This work investigates the magnetic and spectroscopic properties of two recently synthesized complexes and a series of idealized models that incorporate this structural unit. Magnetic interactions, accessible spin states, and 55Mn isotropic hyperfine couplings are computed with quantum chemical methods and form the basis for structure–property correlations. Additionally, the effects of oxo-bridge protonation and one-electron reduction are examined. The calculated properties are found to be in excellent agreement with available experimental data. It is established that all synthetic and model Mn(IV)3CaO4 cubane complexes have the same high-spin S = 9/2 ground state. The magnetic coupling conditions under which different ground spin states can be accessed are determined. Substitution of Mn(IV) magnetic centers by diamagnetic ions [e.g., Ge(IV)] allows one t...
TL;DR: It is demonstrated that the changes in spin states of the metals influence both geometry and vibrational spectra of the complexes, and spectral changes are predicted not only in the low frequency range, corresponding to metal-ligand vibrations, but also in the mid-IR range, where ligand vibrations are active.
Abstract: Possible stable structures of various 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) complexes, [Ni(bpy)(3)](2+), [Co(bpy)(3)](2+), [Fe(bpy)(3)](2+) and Fe(phen)(2)(NCS)(2), were optimized for different spin states of the metals, and the spectra computed for every form were compared with the experimental IR spectra of the compounds. It is demonstrated that the changes in spin states of the metals influence both geometry and vibrational spectra of the complexes. Spectral changes are predicted not only in the low frequency range, corresponding to metal-ligand vibrations, but also in the mid-IR range, where ligand vibrations are active. Detailed computational analysis in combination with the corresponding spectroscopic experiment shows that the spectral changes are of a similar character for complexes with the same ligands independent on the central metal and can be used as spectroscopic markers of the electronic state of the latter. Found spectral markers have been validated at a number of complexes of Fe(II), Ni(II), Co(II), Zn(II) and Cu(II) with bpy and phen ligands.
TL;DR: The molecular spin state of Ni(II) porphyrin, supported on a ferromagnetic Co surface, can be reversibly switched between spin-off and spin-on states upon coordination and decoordination of the gaseous ligand NH3, respectively.
Abstract: Amazing ammonia: The molecular spin state of Ni(II) porphyrin, supported on a ferromagnetic Co surface, can be reversibly switched between spin-off (S = 0) and spin-on (S = 1) states upon coordination and decoordination of the gaseous ligand NH3, respectively (see picture). This finding clearly indicates the possible use of the system as a single-molecule-based magnetochemical sensor and in spintronics.
TL;DR: This work shows how tailoring molecular orbitals can yield all-electrically controlled spintronic device concepts and showcases how a judicious choice of the molecular spin centres determines these critical molecule-electrode contact characteristics.
Abstract: Magnetic molecules are potential functional units for molecular and supramolecular spintronic devices. However, their magnetic and electronic properties depend critically on their interaction with metallic electrodes. Charge transfer and hybridization modify the electronic structure and thereby influence or even quench the molecular magnetic moment. Yet, detection and manipulation of the molecular spin state by means of charge transport, that is, spintronic functionality, mandates a certain level of hybridization of the magnetic orbitals with electrode states. Here we show how a judicious choice of the molecular spin centres determines these critical molecule-electrode contact characteristics. In contrast to late lanthanide analogues, the 4f-orbitals of single bis(phthalocyaninato)-neodymium(III) molecules adsorbed on Cu(100) can be directly accessed by scanning tunnelling microscopy. Hence, they contribute to charge transport, whereas their magnetic moment is sustained as evident from comparing spectroscopic data with ab initio calculations. Our results showcase how tailoring molecular orbitals can yield all-electrically controlled spintronic device concepts.
TL;DR: In this article, the Minnesota density functionals were employed in binding energy calculations for all of the clusters, considering the singlet and triplet spin states for non-defective clusters and doublet and quartet spin state for defective clusters.
Abstract: We consider oxygen interactions with realistic silica surfaces, including both experimentally observed nondefective surface reconstructions and experimentally observed surface defects. Nondefective models include clusters representing the site above a fully coordinated surface Si atom and bridging O atoms, and the defective models include clusters representing an under-coordinated Si defect, a nonbridging O defect, and a ring structure. Energies were obtained for the approach of atomic and molecular oxygen to these clusters in various configurations by using explicitly correlated CCSD(T)-F12b electronic structure theory and the Minnesota density functionals, which were found to be in good agreement. The Minnesota functionals were employed in binding energy calculations for all of the clusters, considering the singlet and triplet spin states for nondefective clusters and doublet and quartet spin states for defective clusters. We find that the chosen defects are energetically favorable sites for binding. Th...