Exchange Interactions In Compounds Research Articles

The Influence of Substitutions in 3d-Sublattice on the Exchange Interactions in Compounds Based on NdMnGe

Magnetic properties of CeFeSi-type NdMn $$_{1-x}$$ Ti $$_{x}$$ Ge compounds studied by magnetization and magnetocaloric measurements are reported. The increase in Ti content leads to the essential increase in magnetic ordering temperature of the Nd sublattice and the magnetocaloric effect. The results are compared with those obtained on isotypic RTX compounds and discussed assuming the itinerant character of magnetism of these compounds.

A new three-dimensional 4,8-connected inorganic open framework based on manganese phosphomolybdate with (41261284) (46)2 topology

Abstract A new inorganic open framework based on manganese phosphomolybdate, (C2N2H10)4{Mn3[P4Mo6O26(OH)5]2}·6H2O (1), has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectroscopy and TG analysis. Single-crystal X-ray diffraction analysis reveals that compound 1 exhibits a 4,8-connected three-dimensional inorganic open framework with (41261284) (46)2 topology and possesses three-dimensional channels filled by the protonated H2en ligands and water molecules. Additionally, DC susceptibility measurement shows the antiferromagnetic character of the exchange interactions in compound 1.

Density functional perturbational orbital theory of spin polarization in electronic systems. II. Transition metal dimer complexes

We present a theoretical scheme for a semiquantitative analysis of electronic structures of magnetic transition metal dimer complexes within spin density functional theory (DFT). Based on the spin polarization perturbational orbital theory [D.-K. Seo, J. Chem. Phys. 125, 154105 (2006)], explicit spin-dependent expressions of the spin orbital energies and coefficients are derived, which allows to understand how spin orbitals form and change their energies and shapes when two magnetic sites are coupled either ferromagnetically or antiferromagnetically. Upon employment of the concept of magnetic orbitals in the active-electron approximation, a general mathematical formula is obtained for the magnetic coupling constant J from the analytical expression for the electronic energy difference between low-spin broken-symmetry and high-spin states. The origin of the potential exchange and kinetic exchange terms based on the one-electron picture is also elucidated. In addition, we provide a general account of the DFT analysis of the magnetic exchange interactions in compounds for which the active-electron approximation is not appropriate.

On the theory of exchange interactions in organometallic compounds. Part I

Recently magnetic order has been found in organometallic donor (D)-acceptor (A) compounds, with a localized spin on a transition-metal ion (donor) and a localized spin on an organic group (acceptor). We call these magnetic d/p systems. The magnetic order is often ferromagnetic. Many of these systems are one-dimensional magnets with a simple structure: ··· D +A −D +A −D + ··· . There are two types of such systems. First, systems in which the localized spins on the donor and acceptor are in orbitals which are not separated by other organic groups, and second systems where there is an intermediate organic group between the donor and acceptor. In this paper we discuss the various contributions to the exchange interaction in the first type of d/p systems. We use the molecular orbital (MO) model applied already successfully by the author and others for the discussion of exchange interactions in transition-metal compounds and rare-earth compounds. The most important contributions to the nearest-neighbour exchange interaction in these compounds come from single-ion exchange on the transition-metal ion between the unpaired spins and spin transferred from the unpaired acceptor spin to occupied and empty atomic transition-metal orbitals. This is the old ferromagnetic Kramers-Anderson mechanism.

Magnetic semiconductors with Curie point above 300 K in the system of the solid solution Cu xMn 1−xCr 2S 4

The magnetic and electric properties of the system of solid solution Cu x Mn 1− x Cr 2S 4 with x = 0, 0.1, 0.2 have been studied. It has been found that the addition of copper into the ferrimagnetic (FIM) semiconductor MnCr 2S 4 results in a strong increase of the Curie temperature T C with the conservation of the semiconductor conductivity. For compositions with x = 0.1 and 0.2, T C is 386 and 398 K, respectively. Thus, we have found new nondegenerate semiconductors with magnetic ordering temperatures higher than room temperature. This strong increase in T C is assumed to be associated with the existence of a strong s-d exchange interaction in compounds with x = 0.1 and 0.2. The value of this interaction has been estimated to be AS ≈ 0.6 eV ( A is the integral of the s-d exchange, S is the Cr 3+ ion spin).

Crystal and molecular structure and magnetic properties of tetrakis-[bromo(2-diethylaminoethanolato)copper(II)]–tetrachloromethane (1/4), a complex with a ferromagnetic ground state

The crystal and molecular structure of [{CuBr(OCH2CH2NEt2)}4]·4CCl4(A) has been determined from three-dimensional X-ray diffractometer data and refined to R 0.061 using 1 581 independent reflections. The tetragonal unit cell of space group I41/a with dimensions a= 19.47(2) and c= 15.78(1)A contains four oxygen-bridged cubane-type clusters of symmetry S4 with a Cu4O4 core. Copper–copper distances are 3.523(2)(× 2), 3.176(2)A(× 4) and copper–oxygen distances 1.924(5)(× 2), 2.524(5)(× 2), and 1.982(5)A(× 4), respectively. The co-ordination around copper (amine nitrogen, bromine, three bridging alkoxide oxygens) is distorted square pyramidal. Sixteen molecules of tetrachloromethane act as solvent of crystallization in the unit cell. The isomorphic [{CuCl(OCH2CH2NEt2)}4]·4CCl4(B) has cell dimensions a= 19.21(2) and c= 15.96(1)A. The decomposition of (A) and (B) has been followed by Debye–Scherrer investigation. The magnetic susceptibility of (A) and (B) in the temperature range 3.4–300 K and of the α and β modifications of [{CuBr(OCH2CH2NEt2)}n](n= 2 or ∞) in the range 70–300 K have also been determined and interpreted in terms of the isotropic Heisenberg–Dirac–van Vleck model. Whereas the α and β modifications show strong antiferromagnetic exchange interaction [2J=–817 and –744 (±20) cm–1], there is simultaneous antiferromagnetic and ferromagnetic exchange interaction in compounds (A) and (B) with the latter interaction dominating. The evaluated exchange parameters are: J12=–4.5 ± 3, J13= 40.0 ± 3 cm–1(A); J12=–5.2 ± 3, J13= 46.9 ± 3 cm–1(B). These can be understood in terms of the Cu–O–Cu bridging angle and the Cu–O bond distances.