Exchange interaction in theYbCrBr93−mixed dimer: The origin of a strongYb3+−Cr3+exchange anisotropy (original) (raw)
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The superexchange interaction between Yb 3ϩ and Cr 3ϩ ions in the mixed YbCrBr 9 3Ϫ bioctahedral facesharing dimer is quantitatively analyzed using a modified kinetic exchange theory, which is adapted to a realistic description of the electronic structure of lanthanide ions in solids. The general procedure of the calculation of the 4 f -3d anisotropic exchange spin Hamiltonian is presented and applied to the YbCrBr 9 3Ϫ dimer. The spin-Hamiltonian of the Yb 3ϩ -Cr 3ϩ exchange interaction is found to be extremely anisotropic,
Exchange interaction between two lanthanide or actinide ions of f 1 configuration bridged by common diamagnetic ligands is theoretically studied using a modified version of the superexchange theory developed in this paper. Exchange spin Hamiltonians were calculated for the M 2 L 10 and M 2 L 11 dimers serving as models of the 90 • and 180 • f 1 –f 1 superexchange, respectively. Spin–orbit coupling and crystal field splitting of the f 1 configuration (resulting in the 7 ground Kramers doublet and the effective spin S = 1 2 of the metal ion), virtual transfers of electrons of the type 4f 1 (A)–4f 1 (B) → 4f 0 (A)–4f 1 (B)5d 1 (B) via ns(L) and np(L) valent orbitals of the bridging ligands, and exchange pathways in these dimers are considered in detail. The f 1 –f 1 superexchange is found to be extremely anisotropic and very sensitive to the geometry of the dimer. The spin Hamiltonian of the M 2 L 10 dimer is H = J x S x A S x B + J y S y A S y B + J z S z A S z B , where the exchange parameters are rationalized in terms of J πσ and J ππ parameters referring, respectively, to the π–σ and π–π pathways of the 4f(A) → np(L) → 5d(B) electron transfers, J x = 2J πσ − J ππ , J y = J πσ + J ππ and J z = −J πσ + J ππ. The J πσ and J ππ values are analytically expressed through 4f|np and 5d|np overlap integrals, orbital energies and intra-ionic Slater parameters. Exchange interaction between f 1 ions in the M 2 L 11 dimer is described by an antiferromagnetic Ising Hamiltonian H = |J ππ |S z A S z B , where the z axis connects two metal ions. Unusual magnetic properties of MUO 3 (M = Li, Na, K and Rb) and Li 3 UO 4 oxides involving U 5+ (5f 1) ions and BaPrO 3 distorted perovskite are discussed in the light of these theoretical results.
Some aspects of configuration interaction of the 4f(N) configurations of tripositive lanthanide ions
The journal of physical chemistry. A, 2014
Some features of the interaction of the 4f(N) configuration of tripositive lanthanide ions (Ln(3+)) with excited configurations have been investigated. The calculated barycenter energies of the same parity 4f(N-1)6p, 4f(N+1)5p(5), and 4f(N-1)5f configurations for Ln(3+), relative to those of 4f(N), are fitted well by exponential functions. The 4f(N) barycenter energies of Ln(3+) in Y3Al5O12/Ln(3+) lie in the band gap, with the exceptions of Tb(3+) and Yb(3+), where they are situated in the conduction and valence bands, respectively. The configuration interaction parameters α, β, and γ, which are fitted in the usual phenomenological Hamiltonian to calculate the crystal field energies of Ln(3+), exhibit quite variable magnitudes in the literature due to incomplete energy level data sets, energy level misassignments and fitting errors. For LaCl3/Ln(3+), 83% of the variation of α and 50% of that for β can be explained by the change in the difference in barycenter energy with the predomi...
Chemical Physics Letters, 2001
The room-temperature magnetic susceptibility anisotropy of eight-coordinate lanthanide ions was modelled numerically for polyhedra resulting from distortions of the regular cube to a tetragonal prism, antiprism, and dodecahedron. Our aim is to illustrate how the magnitude and sign of the room-temperature magnetic anisotropy can be related to the shape of the coordination polyhedron and to estimate its maximum value. Tb(III), Dy(III), and Tm(III) ions are found to have the largest values of the magnetic anisotropy in all coordination polyhedra. These results are helpful to rationalize the orientational behavior of lanthanide-containing liquid crystals in an external magnetic ®eld.
Journal of the American Chemical Society, 2018
Magnetic exchange interactions within the asymmetric dimetallic compounds [hqH][Ln(hq)(NO)]·MeOH, (Ln = Er(III) and Yb(III), hqH = 8-hydroxyquinoline) have been directly probed with EPR spectroscopy and accurately modeled by spin Hamiltonian techniques. Exploitation of site selectivity via doping experiments in Y(III) and Lu(III) matrices yields simple EPR spectra corresponding to isolated Kramers doublets, allowing determination of the local magnetic properties of the individual sites within the dimetallic compounds. CASSCF-SO calculations and INS and far-IR measurements are all employed to further support the identification and modeling of the local electronic structure for each site. EPR spectra of the pure dimetallic compounds are highly featured and correspond to transitions within the lowest-lying exchange-coupled manifold, permitting determination of the highly anisotropic magnetic exchange between the lanthanide ions. We find a unique orientation for the exchange interaction...
Magnetic Anisotropy and Spin-Parity Effect Along the Series of Lanthanide Complexes with DOTA
Angewandte Chemie, 2013
Magnetic anisotropy, arising from the unquenched orbital contribution of the partially occupied inner 4f orbitals combined with the crystal field that breaks the spherical symmetry, is the key property that makes lanthanides a unique ingredient in magnetism. Molecular magnetism makes no exception, especially in the field of bistable materials, like single-molecule magnets (SMM) and single-chain magnets (SCM). In the first case the magnetic anisotropy generates a barrier for the reversal of the magnetization of the molecule that can be overcome either by thermal activation, leading to an exponential growth of the relaxation time at low temperature, or by underbarrier mechanisms, which are severely affected by the symmetry of the crystal field and by the application of an external magnetic field. After the discovery of SMM behavior in a mononuclear Tb sandwich complex with phthalocyaninato ligand an intense research activity has been focused on the design of high-symmetry environments for single lanthanide ions, including polyoxometallate and organometallic sandwich complexes, [7, with the aim to reduce the efficiency of the tunnel mechanism of magnetic relaxation and to increase the blocking temperature of the material. Magneto-structural correlations based on the distribution of the ligand negative charges around the lanthanide ions rely on the generally accepted assumption that the interaction of the magnetic orbitals with the ligand donor atoms is electrostatic, given the inner character of the 4f electrons. Rinehart and Long have recently associated the presence/ absence of SMM behavior in complexes of tripositive lanthanides to the combination of the spatial distribution of negative charges of the 4f electrons with that of the ligands donor atoms. The geometry of the 4f orbitals, can be prolate (elongated), oblate (flattened), or spherical. Easy axis, or Ising, magnetic anisotropy, a prerequisite for observing magnetic bistability, is favored when the ligand field stabilizes the state with the largest projection of the total angular momentum, J. This occurs for oblate ions with ligands that concentrate the negative charges in an axial position, while equatorial ligands are predicted to favor SMM behavior in prolate ions.
We report here the synthesis and the investigation of the magnetic properties of a series of binuclear lanthanide complexes belonging to the metallacrown family. The isostructural complexes have a core structure with the general formula [Ga 4 Ln 2 (shi 3À ) 4 (Hshi 2À ) 2 (H 2 shi À ) 2 (C 5 H 5 N) 4 (CH 3 OH) x (H 2 O) x ]$ xC 5 H 5 N$xCH 3 OH$xH 2 O (where H 3 shi ¼ salicylhydroxamic acid and Ln ¼ Gd III 1; Tb III 2; Dy III 3; Er III 4; Y III 5; Y III 0.9 Dy III 0.1 6). Apart from the Er-containing complex, all complexes exhibit an antiferromagnetic exchange coupling leading to a diamagnetic ground state. Magnetic studies, below 2 K, on a single crystal of 3 using a micro-squid array reveal an opening of the magnetic hysteresis cycle at zero field.
Chemistry - A European Journal, 2013
After the seminal discovery of slow relaxation and quantum tunneling of magnetization in Mn 12 OAc, [1] the field of molecular magnetism has received fast-growing attention. A particular focus lies in the design of single-molecule magnets (SMMs) that are desired to possess ever longer magnetization relaxation times at ever higher blocking temperatures. Here, magnetic anisotropy plays a key role. [3] In 3d metal ions, single-ion anisotropies are typically small because the orbital momentum is often quenched by the ligand field, and thus, anisotropy only appears through second-order perturbation effects. In contrast, when the first-order contribution can be exploited, the anisotropy is strongly enhanced. In this sense 4d, 4f, or 5d metal ions are more appropriate for introducing anisotropy than most of their 3d congeners. Indeed, much effort has been devoted to the synthesis of 4f SMMs, which currently possess the longest magnetization relaxation times among molecular clusters. However, the well-shielded 4f shell of the lanthanides mostly results in weak magnetic exchange interactions, and hence, the use of 4d and 5d ions to build exchange-coupled clusters and SMMs can be advantageous. The 4d and 5d orbitals are more diffuse than the 3d orbitals, enabling stronger exchange coupling to neighboring ions. Notably, to date, the strongest ferromagnetic coupling observed through the cyanide ion is found in the Re IV À Cu II chain (nBu 4 N)-Cl 4 (CN) 2 ]·1.33 CH 3 CN (Tp À = hydrotris(pyrazol-1-yl)borate) with ÀJ = + + 29 cm À1 (in the À2JS 1 ·S 2 Hamiltonian definition). The angular momentum of half-integer spin 4d, 4f, and 5d ions is often described by using a t = 1/2 pseudospin approach, only taking into account the lowest doublet. Then the magnetic anisotropy induced by a ligand field enters by anisotropic exchange interactions, but orbitally dependent exchange can also give rise to anisotropic interactions. Despite the expected large anisotropies and possibly enhanced SMM properties, very few SMMs are based on 4d and 5d
Extraction of crystal-field parameters for lanthanide ions from quantum-chemical calculations
Journal of Physics: Condensed Matter, 2011
A simple method for constructing effective Hamiltonians for the 4f N and 4f N-1 5d energy levels of lanthanide ions in crystals from quantum-chemical calculations is presented. The method is demonstrated by deriving crystal-field and spin-orbit parameters for Ce 3+ ions doped in LiYF 4 , Cs 2 NaYCl 6 , CaF 2 , KY 3 F 10 and YAG host crystals from quantum chemical calculations based on the DV-Xα method. Good agreement between calculated and fitted values of the crystal-field parameters is obtained. The method can be used to calculate parameters even for low-symmetry sites where there are more parameters than energy levels.
Multipolar exchange interaction and complex order in insulating lanthanides
Physical Review B, 2022
In insulating lanthanides, unquenched orbital momentum and weak crystal-field (CF) splitting of the atomic J multiplet at lanthanide ions result in a highly ranked (multipolar) exchange interaction between them and a complex low-temperature magnetic order not fully uncovered by experiment. Explicitly correlated ab initio methods proved to be highly efficient for an accurate description of CF multiplets and magnetism of individual lanthanide ions in such materials. Here we extend this ab initio methodology and develop a first-principles microscopic theory of multipolar exchange interaction between J-multiplets in f metal compounds. The key point of the approach is a complete account of Goodenough's exchange mechanism along with traditional Anderson's superexchange and other contributions, the former being dominant in many lanthanide materials. Application of this methodology to the description of the ground-state order in the neodymium nitride with rocksalt structure reveals the multipolar nature of its ferromagnetic order. We found that the primary and secondary order parameters (of T1u and Eg symmetry, respectively) contain non-negligible Jtensorial contributions up to the ninth order. The calculated spin-wave dispersion and magnetic and thermodynamic properties show that they cannot be simulated quantitatively by confining to the ground CF multiplet on the Nd sites. Our results demonstrate that the ab initio approach to the low-energy Hamiltonian represents a powerful tool for the study of materials with complex magnetic order.