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Exchange Integrals (exchange + integral)

Distribution by Scientific Domains

Chemistry	53%

Selected Abstracts

Magnetic and Electrochemical Properties of a Heterobridged ,-Phenoxido,,1,1 -Azide Dinickel(II) Compound: A Unique Example Demonstrating the Bridge Distance Dependency of Exchange Integral

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2009
Rajesh Koner
Abstract The synthesis, structure, magnetic and electrochemical properties of the heterobridged ,-phenoxido,,1,1 -azide dinickel(II) compound [NiII2(HL1)3(,1,1 -N3)]·3H2O (1) derived from the tetradentate Schiff base ligand N -(2-hydroxyethyl)-3-methoxysalicylaldimine (H2L1) are described. The title compound crystallizes in the triclinic system (space group P). Electrochemical analyses reveal that compound 1 exhibits two-step quasireversible couples in the reduction window with E1/2 values of ,1412 and ,1762 mV. The variable-temperature (2,300 K) magnetic susceptibilities at 1 T of the title compound were measured. The interaction between the metal centres is weak ferromagnetic (J = 5.0 cm,1, g = 2.23, D1 = 29.2 cm,1 and D2 = 10.7 cm,1). Comparison of the exchange integral of 1 with that of the only reported ,-phenoxido,,1,1 -azide dinickel(II) compound results in the emergence of a unique example of the dependence of strength of magnetic exchange interaction on the metal,ligand bridge distance. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Estimation of effective exchange integral value of polyradical systems based on the band calculation

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2009
Yasuyuki Nakanishi
Abstract Effective exchange integral (Jab) values calculated by cluster models were compared with values calculated under the periodic boundary conditions. So far, to estimate the Jab value of a macro system, we have considered that of the corresponding to cluster one. However, they will get absolutely nothing out of it if a cluster model and the periodic boundary conditions method give different results to us. The main aim of this report is to give an opinion to this issue using a one-dimensional polyhydrogen system as example. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]

The changes of magnetic properties of the perovskite-type titanium oxides by the structural distortions: In the case of LaTiO3 and YTiO3

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2007
Taku Onishi
Abstract In the perovskite-type titanium oxides, the changes of magnetic properties by GdFeO3 -type lattice distortion are observed. In this study, we have performed cluster model calculations based on the density functional theory method, and have obtained the effective exchange integral (Jab) in order to elucidate the magnetic change by the GdFeO3 -type lattice distortion. The components of deciding the orbital ordering and magnetic property have also been discussed. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]

Theory of chemical bonds in metalloenzymes III: Full geometry optimization and vibration analysis of ferredoxin-type [2Fe,2S] cluster

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2007
Mitsuo Shoji
Abstract The nature of chemical bonds in a ferredoxin-type [2Fe,2S] cluster has been investigated on the basis of natural orbitals and several bond indices developed in Parts I and II of this study. The broken-symmetry hybrid density functional theory (BS-HDFT) with spin projection approach has been applied to elucidate the natural orbitals and occupation numbers for a model compound [Fe2S2(SCH3)4] (1), which is used to calculate the indices. The molecular structure, vibration frequencies, electronic structures, and magnetic properties in both oxidized and reduced forms of 1 have been calculated and compared with the experimental values. The optimized molecular structures after approximate spin projection have been in good agreement with experimental data. The structure changes upon one-electron reduction have been slight (<0.1 Å) and only limited around one side of the Fe atom. Raman and infrared (IR) spectra have been calculated, and their vibration modes have been assigned using the bridging 34S isotope substitution. Their magnetic properties have been examined in terms of spin Hamiltonians that contain exchange interactions and double exchange interactions. The BS-HDFT methods have provided the magnetic parameters; i.e., effective exchange integral (J) values and valence delocalization (B) values, which agree with the experimental results. It is found that large charge transfer (CT) from the bridging sulfur to the iron atoms has led to the strong antiferromagnetic interactions between iron atoms. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]

One-dimensional disordered magnetic Ising systems: A new approach

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2009
Vladimir Gasparian
Abstract We reconsider the problem of a one-dimensional Ising model with an arbitrary nearest-neighbor random exchange integral, temperature, and random magnetic field in each site. A convenient formalism is developed that reduces the partition function to a recurrence equation, which is convenient both for numerical as well as for analytical approaches. We have calculated asymptotic expressions for an ensemble averaged free energy and the averaged magnetization in the case of strong and weak couplings in external constant magnetic field. With a random magnetic field at each site in addition to nearest-neighbor random exchange integrals we also evaluated the free energy. We show that the zeros of the partition function for the Ising model in the complex external magnetic field plane formally coincide with the singularities of the real part of electron's transmission amplitude through the chain of , -function potentials. [source]

Evaluation of Two-center One- and Two-electron Integrals over Slater Type Orbitals

CHINESE JOURNAL OF CHEMISTRY, Issue 5 2006
Yusuf Yakar
Abstract A formulation previously presented by the authors for coulomb integrals was generalized to other two-center integrals, except exchange integral. Within this frame, molecular integrals were expressed in terms of some new functions closely related to the well-known incomplete gamma functions and these functions recursively evaluated. Special issues arising in the case of hybrid integrals were addressed, and the results were compared with the ones found in the literature. [source]

Syntheses, Structures and Magnetic Properties of Trinuclear CuIIMIICuII (M = Cu, Ni, Co and Fe) and Tetranuclear [2×1+1×2] CuIIMnII,2CuII Complexes Derived from a Compartmental Ligand: The Schiff Base 3-Methoxysalicylaldehyde Diamine Can also Stabilize a Cocrystal

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2010
Arpita Biswas
Abstract The present investigation describes syntheses, characterization and studies of the mononuclear compound [CuIIL,(H2O)] (1), the triangular, trinuclear monophenoxido-bridged compounds [{CuIIL}2MII(H2O)2](ClO4)2·nH2O [2 (M = Cu, n = 0), 3 (M = Ni, n = 3), 4 (M = Co, n = 0), 5 (M = Fe, n = 0)] and the tetrametallic self-assembled complex [{CuIILMnII(H2O)3}{CuIIL}2](ClO4)2·H2O (6) derived from compartmental Schiff base ligand, H2L, which is the [2+1] condensation product of 3-methoxysalicylaldehyde and trans -1,2-diaminocyclohexane. Single-crystal X-ray structures of 2, 5 and 6 were determined. Two pairs of terminal···central metal ions in the trinuclear cores in 2 and 5 are monophenoxido-bridged. Interestingly, the CuO6 and FeO6 environments have tetragonally compressed octahedral geometries. On the other hand, the structure of 6 reveals that it is a [2×1+1×2] cocrystal of one diphenoxido-bridged dinuclear [CuIILMnII(H2O)3]2+ dication and two mononuclear [CuIIL] moieties. Cocrystallization in 6 takes place as a result of water encapsulation. The variable-temperature (2,300 K) magnetic susceptibilities of compounds 2,6 have been measured. The exchange integrals obtained are: the CuII3 compound 2, J = ,78.9 cm,1; the CuIINiIICuII compound 3, J = ,22.8 cm,1; the CuIICoIICuII compound 4, J = ,7.8 cm,1; the CuIIFeIICuII compound 5, J = ,3.0 cm,1; the CuII3MnII compound 6, J = ,15.1 cm,1. The monophenoxido-bridging core in 3 and 4 has been proposed after comparison of the structures and magnetic properties of these two compounds with those of 2, 5 and related other compounds. This paper presents rare examples of monophenoxido-bridged CuIIMIICuII (M = Cu, Ni, Co and Fe) compounds, provides an understanding of the structures from magnetic exchange integrals, and, most importantly, reports on the first example of a cocrystal derived from a 3-methoxysalicylaldehyde diamine compartmental ligand. [source]

Raman scattering studies of the magnetic ordering in hexagonal HoMnO3 thin films

JOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2010
Nguyen Thi Minh Hien
Abstract We present the results of the temperature dependence of the Raman spectra of hexagonal HoMnO3 thin films in the 13,300 K temperature range. The films were grown on Pt(111)//Al2O3 (0001) substrates using the laser ablation method. In the HoMnO3 thin films, we initially observedseveral broad Raman peaks at ,510, 760, 955, 1120, and 1410 cm,1. These broad Raman peaks display an anomalous behavior near the magnetic transition temperature, and the intensity difference of the Raman spectra at different temperatures shows several pairs of negative and positive peaks as the temperature is lowered below the Néel temperature. Our analyses indicate that all the broad peaks are correlated with magnetic ordering, and we have assigned the origin of all the broad peaks. Purely on the basis of the Raman analysis, we have deduced the Néel temperature and the spin exchange integrals of HoMnO3 thin films. We also investigated the effects of the growth condition on the strongest broad peak at ,760 cm,1, which is related with pure magnetic ordering. This result indicates that the oxygen defect in the HoMnO3 sample has negligible effect on magnetic ordering. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Domains in helicoidal magnetic structure

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2010
E. V. Rosenfeld
Abstract Theoretical investigation of the magnetic spiral behavior in a layered magnet with strong hexagonal magnetic anisotropy has been performed. It is shown that if the exchange integrals between the first and second neighboring layers meet the requirement |J1|,=,,J2, the energy densities for spirals with three and four (at J1,<,0) or four and six (at J1,>,0) layers in the period coincide. Moreover, near the surface of contact of the above phases the energy density is equal to or even lower than inside each of them, which should result in the appearance of a domain magnetic structure. [source]

One-dimensional disordered magnetic Ising systems: A new approach

Effects of dilution and disorder on magnetism in diluted spin systems

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007
Guixin Tang
Abstract The influence of configurational disorder on the magnetic properties of diluted Heisenberg spin systems is studied with regard to the ferromagnetic stability of diluted magnetic semiconductors. The equation of motion of the magnon Green's function is decoupled by Tyablikov approximation. With supercell approach, the concentrations of magnetic ions are determined by the size of the supercell in which there is only one magnetic ion per supercell in our method. In order to distinguish the influence of dilution and disorder, there are two kinds of supercells being used: the diluted and ordered case and the diluted and disordered case. The configurational averaging of magnon Green function due to disorder is treated in the augmented space formalism. The random exchange integrals between two supercells are treated as a matrix. The obtained magnon spectral densities are used to calculate the temperature dependence of magnetization and Curie temperature. The results are shown as following: (i) dilution leads to increasing the averaged distance of two magnetic ions, further decreases the effective exchange integrals and is main reason to reduce Curie temperature; (ii) spatial position disorder of magnetic ions results in the dispersions of the exchange integrals between two supercells and slightly changes ferromagnetic transition temperature; (iii) the exponential damping of distance dependence obviously reduces Curie temperature and should be set carefully in any phenomenological model. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magneto-optical spectroscopy of (Zn,Co)O epilayers

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2006
W. Pacuski
Abstract We present a magneto-optical study of (Zn,Co)O layers grown by molecular beam epitaxy. We observed sharp lines related to 4A2,2E intra-ionic Co2+ transitions, and to the A , B and C excitons. Intra-ionic transitions observed by absorption and photoluminescence were used to determine the values of the parameters describing the isolated Co ions, such as the easy-plane magnetic anisotropy and the g -factor of the S = 3/2 Cobalt spin. Excitonic transitions observed in reflectivity were used to determine the giant Zeeman splitting and to estimate the effective coupling ,N0(, , , ),A ,B = 0.4 eV between excitons and Cobalt spins. Due to the electron,hole exchange within the exciton, this effective spin,exciton coupling is much weaker than the exchange integrals for free carriers, estimated to be N0|, , , | , 0.8 eV, with a positive value of (, , , ) if the normal ordering of the valence band of ZnO is assumed. The Zeeman splitting of diluted samples and the magnetic circular dichroism (for a higher Co content) are proportional to the magnetization of the paramagnetic, isolated Cobalt ions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

On the strength of the double exchange and superexchange interactions in La0.67Ca0.33Mn1,yFeyO3 , an NMR and Mössbauer study

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006
J. Przewo
Abstract A combined study of La0.67Ca0.33Mn0.9757Fe0.03O3 compound by means of zero field 55Mn and 57Fe NMR as well as 57Fe Mössbauer spectroscopy (MS) is reported. The 55Mn NMR spectra exhibit a single double exchange (DE) line up to the magnetic ordering temperature (TC), 200 K, determined from magnetization measurements. The hyperfine field (HFF) remains finite at the TC, which reveals discontinuous character of the transition and the occurrence of a ferromagnetic-paramagnetic phase segregation. The 57Fe MS HFF decreases much faster with increasing temperature than the 55Mn NMR HFF. Application of a molecular field model to the temperature dependence of the 55Mn and 57Fe HFF allows to estimate values of the Mn,Mn and the Fe,Mn exchange integrals, which amount to 1.24 meV and ,0.6 meV, respectively. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]