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Magnetic Interactions (magnetic + interaction)

Distribution by Scientific Domains

Chemistry	56%
Physics and Astronomy	43%

Selected Abstracts

Towards a Better Understanding of Magnetic Interactions within m -Phenylene ,-Nitronyl Nitroxide and Imino Nitroxide Based Radicals, Part III: Magnetic Exchange in a Series of Triradicals and Tetraradicals Based on the Phenyl Acetylene and Biphenyl Coupling Units

CHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2005
Laure Catala Dr.
Abstract The present work completes and extends our previous reports1,,2 on the determination of the magnetic ground state and on the strength of the through bond exchange coupling within series of biradicals. This knowledge was subsequently exploited for the analysis of the magnetic interactions in their crystals. We report here the studies of series of triradicals incorporating ,-nitronyl nitroxides (NN) or ,-imino nitroxides (IN) as terminal radical fragments connected through a m -phenylene coupling unit in one case and a phenyl acetylene unit in other case. Tetraradical derivatives have also been studied. The studies of isolated molecules (EPR in solution and DFT calculations) allow the assessment of the magnetic interactions through the magnetic coupling unit. All triradical derivatives are found to exhibit a quartet ground state, whereas a singlet ground state is determined for the tetraradical. This last result reinforces previous findings that the singlet ground state is favoured in related biradicals involving similar m -phenylene couplers. Moreover, the through bond magnetic exchange coupling for the ortho,meta connectivity could be demonstrated as being ferromagnetic, thus ascertaining our previous hypotheses.1 The magnetic properties of the triradicals and tetraradicals in their solid state have been rationalized by using a previously proposed methodology,2 allowing to identify the most relevant magnetic pathways. Le présent travail complète et étend nos travaux précédents portant sur la détermination des couplages d'échange magnétique intramoléculaires de séries de biradicaux,1,,2 et partant de cette connaissance, de l'analyse des corrélations magnétostructurales dans l'état cristallin. Nous présentons ici l'étude de séries de triradicaux comprenant des radicaux , -nitronyl nitroxydes (NN) ou , -imino nitroxydes (IN) substitués en méta d'un groupement phénylène d'une part, et en para d'un groupement phénylène éthynylène d'autre part. Des dérivés tétraradicalaires ont aussi été synthétisés et étudiés. Les interactions d'échange magnétique à travers les liaisons sont estimées d'après l'étude de ces molécules isolées par RPE en solution ainsi que par des calculs effectués dans l'approximation de la fonctionnelle densité (DFT). Alors que l'ensemble des dérivés triradicalaires présente un état fondamental magnétique quartet de spin, un état singulet est proposé pour les tétraradicaux. Ce dernier résultat confirme nos travaux précédents1 ayant conclu à un état fondamental singulet pour des biradicaux basés sur le même coupleur. De plus, le couplage d'échange magnétique au travers du coupleur phénylène éthynylène pour des biradicaux substitués dans une topologie ortho,méta est ferromagnétique, confirmant ainsi les hypothèses antérieures.1 Suivant une méthodologie précédemment décrite,2 les propriétés magnétiques des triradicaux à l'état cristallin ont pu être analysées dans le détail et permettent de proposer des chemins d'interaction magnétique et des géométries de contacts intermoléculaires précises pour l'établissement d'interactions magnétiques bien identifiées. El presente trabajo completa y extiende nuestras anteriores estudios1,,2 sobre la determinacion del estado fundamental magnético y la fuerza del intercambio magnetico a través del enlace en una serie de biradicales. Esta información es luego usada en el análisis de las interacciones magneticas dentro de sus cristales. En este trabajo presentamos los estudios sobre una serie de triradicales que contienen , -nitroxidos nitronílicos (NN) o , -imino nitróxidos (IN) como fragmentos radicalarios terminales conectados a través de unidades acopladoras del tipo m -phenilénicas, en un caso, y fenil acetilénicas, en el otro. Se han estudiado también tetraradicales. Los estudios con moleculas aisladas (EPR en disolución y DFT) permiten evaluar las interacciones magneticas a través de las unidades acopladoras. Todos los triradicales se ve que presentan un estado fundamental del tipo cuadruplete, mientras que el cuadruplete se cree que tienen un estado fundamental singlete. Este último resultado refuerza las conclusiones de un estudio previo en el que se vió que el singlete es el estado fundamental en biradicales similares conectados por una unidad m -fenilénica. Además, el intercambio magnético a través del enlace para la conectividad orto y meta se demuestra que es ferromagnetica, confirmando hipótesis anteriores.1 Las propiedades magnéticas de los triradicales y tetraradicales en su estado sólido se han racionalizado empleando una matodología propuesta anteriormente,2 identificando los caminos magnéticos relevantes. [source]

Magneto,Structural Correlations in Discrete MnII -WV Cyano-Bridged Assemblies with Polyimine Ligands

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 26 2010
Robert Podgajny
Abstract We present the magneto,structural correlations for two novel discrete cyano-bridged assemblies based on cationic complexes of manganese(II) with diimine ligands and octacyanotungstate(V) ions. The crystal structure of [MnII(terpy)(dmf)(H2O)2][MnII(terpy)(H2O)(dmf)(,-NC)WV(CN)7]2·6H2O (1) (terpy = 2,2,;6,,2,-terpyridine, dmf = dimethylformamide) contains dinuclear {MnIIWV}, cyano-bridged anions, while the crystal structure of [MnII(phen)3]2[MnII(phen)2(,-NC)2WV(CN)6]2(ClO4)2·9H2O (2) (phen = 1,10-phenanthroline) is built of tetranuclear {MnII2WV2}2, square anions. Intramolecular Mn,W magnetic interactions through the cyano bridges are represented by magnetic coupling constants J = ,39 cm,1 for the {MnIIWV}, unit in 1 and J1 = ,25.7 and J2 = ,16.7 cm,1 for the {MnII2WV2}2, unit in 2. J and J1 represent relatively strong W,CN,Mn interactions and are ascribed to the bridges in b positions of TPRS-8 (trigonal prism square-face bicapped) of [W(CN)8]3, polyhedra, favoring the strongest electronic interactions between the d,d orbital of W and the ,* orbitals of CN,, whereas J2 is related to the m vertex of [W(CN)8]3,. The magnetic properties of 1 and 2 are compared with reference compounds and discussed in the context of the type of coordination polyhedra of [W(CN)8]3, as well as the metric parameters of cyano-bridged W,CN,Mn linkages. We found the type of coordination polyhedra and bridging mode of [W(CN)8]3, to be the most important factors influencing the magnitude of the Mn,W magnetic interaction. [source]

A Theoretical Study of Correlation between Hydrogen-Bond Stability and J -Coupling through a Hydrogen Bond

HELVETICA CHIMICA ACTA, Issue 10 2003
Shun-ichi Kawahara
trans -Hydrogen-bond hyperfine splitting via magnetic interaction, which is observed as J -coupling in NMR experiments, was theoretically studied. trans -Hydrogen-bond hyperfine splitting should be closely related to the orbital interaction between the lone-pair orbital of the H-bond acceptor and the antibond orbital of the H-bond donor. A linear relationship was observed between magnetic interaction hyperfine splitting through a H-bond and the H-bond strength. The relationship was dependent on the type of the nucleus forming the H-bond; linear correlation was observed in NH,,,O/N type or OH,,,N type H-bonded complexes, but not in OH,,,O type H-bonded complexes. [source]

Interlayer coupling in magnetic superlattices with electron density inhomogeneities

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2004
W. Gruhn
Abstract We discuss the influence of spatial inhomogeneities of the free electron density on the magnetic interaction between magnetic layers of the superlattice, mediated across nonmagnetic, metallic spacer. Using the modified total energy approach, we prove that the TM or RE superlattices the additional scattering of free electrons on magnetic ion multipole moment increases the ferroquadrupolar biquadratic coupling between magnetic layers. It is shown also that the nonuniform free electron density generates contribution to the interlayer coupling being of the Dzialoshinsky-Moriya type. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

EPR studies on Na-oleate coated Fe3O4 nanoparticles

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004
Y. Köseo
Abstract Superparamagnetic iron oxide nanoparticles were prepared by the co-precipitation technique. Then, fine iron oxide nanoparticles were coated by Na-oleate. Magnetic properties of Na-oleate coated and uncoated iron oxide nanoparticles were investigated by Electron Paramagnetic Resonance (EPR) technique. At room temperature, a single, strong and broad EPR signal was observed for both samples with effective g-values of 2,0839 and 2,18838 for coated and uncoated samples, respectively. The intensity, line width and the resonance field for both coated and uncoated samples are strongly temperature dependent. When the sample is coated with Na-oleate, the line width and the resonance field values of the EPR signal increase due to the decrease in the magnetic interaction between the particles. The total effective magnetic moment of such coated particles is found to decrease, which is most likely due to a non-collinear spin structure originated from the pinning of the surface spins and coated surfactant at the interface of nanoparticles. [source]

Luminescence spectra in metallic and ferromagnetic GaMnAs/GaAs multilayers: a self-consistent super-cell Kane k.p calculation

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2004
G. M. Sipahi
Abstract We present a self-consistent Kane k.p calculation for obtaining the luminescence spectra of GaMnAs/GaAs multilayers. Our model consists of substitutional Mn ions uniformly distributed in GaMnAs layers of width d1 at a concentration of 5%. The high Mn concentration allows to approximating the density of the magnetic moments by a continuous distribution when treating the magnetic interaction between holes and the localized moment on the Mn++ sites. These DMS layers are assumed to be ferromagnetic, at T = 0 K, metallic, and with a hole concentration equivalent, in bulk, to 1 × 1020 cm,3. The DMS layers are separated by non-magnetic GaAs layers. The magnetization is kept perpendicular-to-the-plane (parallel to the growth direction) by the application of a weak magnetic field, which does not affect the electronic structure directly. The luminescence spectrum is obtained for several numbers of DMS layers in the structure. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magneto,Structural Correlations in Discrete MnII -WV Cyano-Bridged Assemblies with Polyimine Ligands

Synthesis, Structural, Thermal and Magnetic Characterization of a Pyrophosphato-Bridged Cobalt(II) Complex

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2008
Oluwatayo F. Ikotun
Abstract The reaction in water of CoII sulfate heptahydrate with 1,10-phenanthroline (phen) and sodium pyrophosphate (Na4P2O7) in a 2:4:1 stoichiometric ratio resulted in the crystallization of a neutral dinuclear CoII complex, {[Co(phen)2]2(,-P2O7)}·6MeOH (1), as revealed by a single-crystal X-ray diffraction study. The bridging pyrophosphato ligand between the two [Co(phen)2]2+ units in a bis(bidentate) coordination mode places the adjacent metal centers at 4.857 Å distance, and its conformation gives rise to intramolecular ,,, stacking interaction between adjacent phen ligands. Indeed, intermolecular ,,, stacking interactions between phen ligands from adjacent dinuclear complexes create a supramolecular 2D network in 1. Magnetic susceptibility measurements on a polycrystalline sample of 1 in the temperature range 1.9,295 K are typical of an overall antiferromagnetic coupling with a maximum of the magnetic susceptibility at 3.0 K. The analysis of the magnetic data in the whole temperature range allows the determination of the value of the intramolecular magnetic coupling (J = ,1.23 cm,1). The ability of the pyrophosphato ligand to mediate magnetic interactions between different first-row transition-metal ions when adopting the bis(bidentate) bridging mode is analyzed and discussed in the light of the small number of magneto-structural reports on this type of compound, bearing in mind the number of unpaired electrons and type of magnetic orbitals on each metal center. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Nickel-Organic Coordination Layers with Different Directional Cavities

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2006
Youfu Zhou
Abstract The two new metal-organic coordination frameworks [Ni2(pydc)2(4,4,-bpy)(H2O)4]n·0.5n(4,4,-bpy)2H2O (1) and [Ni2(pydc)2(2,2,-bpy)2(H2O)2]n·2nH2O (2) (H2pydc = pyridine-3,4-dicarboxylic acid; bpy = bipyridine) have been synthesised under hydrothermal conditions and characterised by single-crystal X-ray diffraction analysis. The structure of 1 contains parallel rectangular channels that accommodate large 4,4,-bpy guests while that of 2 contains vertical channels coordinated to 2,2,-bpy ligands. Their magnetic analyses show that they exhibit different magnetic interactions. The red shifts of the peak in their emission spectra relative to those of the the free ligands could be attributable to the metal,ligand coordination. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Hybrid Magnetic Materials Based on Nitroxide Free Radicals and Extended Oxalato-Bridged Bimetallic Networks

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2005
Antonio Alberola
Abstract A series of hybrid organic-inorganic magnets of formula p -rad[MIICr(ox)3] [M = Mn (1), Co (2), Ni (3), Zn (4)] and m -rad[MIICr(ox)3] [M = Mn (5), Co (6)], in which N -methylpyridinium cations bearing a nitronyl nitroxide moiety in positions 3 (m -rad) or 4 (p -rad) of the pyridine ring coexist with the 2D honeycomb-like oxalato-bridged bimetallic lattice, has been prepared and studied by AC and DC magnetic susceptibility measurements and EPR spectroscopy. In general, the physical properties of these magnets are not altered significantly by the insertion of the nitronyl nitroxide radicals although these paramagnetic molecules seem to interact weakly with the inorganic network as demonstrated by EPR spectroscopy. Some differences can also be observed between the p -rad and m -rad series, i.e. m -rad derivatives have smaller values for the critical temperatures and coercive fields. We also report on the X-ray crystal structures and magnetic properties of p -rad[Mn(H2O)Cr(ox)3]·2H2O (7) and m -rad[Mn(H2O)2Cr(ox)3]·2H2O (8), two extended oxalato-bridged compounds with new topologies. Compound 7 is antiferromagnetic and its structure is a 3D achiral lattice in which zigzag ferromagnetic MnCr chains (J/k = +0.8 K) are interconnected to form hellicoidal hexagonal channels with the cationic free radicals residing in the free space. Compound 8, however, exhibits a ladder-like structural pattern with competing magnetic interactions and paramagnetic behaviour down to low temperatures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Theoretical studies on effects of hydrogen bonds attaching to cysteine ligands on 4Fe-4S clusters

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2008
Y. Kitagawa
Abstract The effect of hydrogen bonds attaching to sulfur atoms of cysteine ligands on 4Fe-4S cluster is examined by using UB3LYP method. Calculated results indicate that an existence of the hydrogen bonds scarcely changes SOMO-SUMO gap, shapes of Kohn-Sham orbitals, and magnetic interactions between Fe ions, although it stabilizes Kohn-Sham orbital energies of SOMO and SUMO about 1.0 eV. And they also make a reduced state stable in comparison with an oxidized state. In addition, the point charges of +0.1e (e: elementary electric charge) at the position of the hydrogen atoms give almost same results to the hydrogen bonds quantitatively. The results suggest that a positive environment from the hydrogen bonds around the clusters is important for a redox potential of 4Fe-4S clusters. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

Theory of chemical bonds in metalloenzymes.

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2008

Abstract A first principle investigation has been carried out for intermediate states of the catalytic cycle of a cytochrome P450. To elucidate the whole catalytic cycle of P450, the electronic and geometrical structures are investigated not only at each ground state but also at low-lying energy levels. Using the natural orbital analysis, the nature of chemical bonds and magnetic interactions are investigated. The ground state of the Compound 1 (cpd1) is calculated to be a doublet state, which is generated by the antiferromagnetic coupling between a triplet Fe(IV)O moiety and a doublet ligand radical. We found that an excited doublet state of the cpd1 is composed of a singlet Fe(IV)O and a doublet ligand radical. This excited state lies 20.8 kcal mol,1 above the ground spin state, which is a non-negligible energy level as compared with the activation energy barrier of ,E# = 26.6 kcal mol,1. The reaction path of the ground state of cpd1 is investigated on the basis of the model reaction: 3O(3p) + CH4. The computational results suggest that the reactions of P450 at the ground and excited states proceed through abstraction (3O-model) and insertion (1O-model) mechanisms, respectively. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

Charge-induced modulation of magnetic interactions in a [2 × 2] metal-organic grid complex,

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2006
C. Romeike
Abstract We investigate the magnetic state of a recently synthesized [2 × 2]-metal-organic grid complex as a function of its redox state. Our analysis of a phenomenological model for the relevant molecular orbitals reveals that additional electrons on the ligands can couple their spins via the bridging metal sites. We find that at certain stages of the reduction of the complex cation, a maximal total spin ground state of the complex (S = 3/2) can be stabilized by the Nagaoka mechanism. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]

The dynamic behavior of magnetic colloids in suspension

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007
Tina Autenrieth
The dynamic behavior of magnetic colloidal particles in suspension is investigated. The particles of the core,shell colloid consist of a cobalt ferrite core embedded in a silica shell and are stabilized by surface charges. As the suspension is strongly opaque to visible light, it can not be probed by dynamic light scattering techniques as a result of strong multiple scattering as well as absorption effects. Therefore, the static and dynamic behavior is probed with small-angle X-ray scattering and X-ray photon correlation spectroscopy (XPCS), respectively. Using XPCS, we are able to study the diffusion coefficient of an opaque colloidal system as a function of the scattering vector. In this paper, we report on the behavior of the colloidal system in the absence of an external magnetic field, meaning that the magnetic moments of the particles are oriented randomly. We find no evidence for magnetic interactions in the static data, while the dynamic XPCS data deviate very significantly from the predictions of model calculations. [source]

Porous silicon/metal nanocomposite with tailored magnetic properties

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009
Petra Granitzer
Abstract Porous silicon (PS) templates in the meso/macro porous regime with oriented pores clearly separated from each other and filled in a galvanic deposition process with various metals, especially ferromagnetic ones are magnetically investigated. The employment of different metals (e.g. Ni, Co, NiCo) together with the variation of the electrochemical deposition parameters modifies the structural characteristics of the PS/metal nanocomposite and thus leads to distinct magnetic properties of the hybrid system. Furthermore the use of different PS-templates which means a change of the pore-diameter and interpore spacing results also in various magnetic characteristics, especially influences on the magnetic interactions among the deposited metal nanostructures. Therefore the specimens show tailored magnetic properties like coercivity, squareness and magnetic anisotropy. The achieved nanocomposite merges electronic properties of a semiconductor with nanomagnetism and therefore opens the possibility of integrated spin-based electronic devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ferromagnetic nanoparticles embedded in self-arranged matrices

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2008
K. Rumpf
Abstract The investigated nanoscopic system, consisting of a non magnetic host material and precipitated ferromagnetic nanostructures shows a magnetic behaviour correlated to the size and shape of the deposited particles but also to their spatial distribution within the template which modifies the magnetic interactions between them. The nanostructures are deposited electrochemically into an etched silicon wafer exhibiting an array of channels of a few ten nanometers in diameter and a length up to 50 µm. The self-assembled grown templates offer the opportunity of tuning the magnetic properties by varying the geometrical characteristics of the membrane which can be loaded with different metals like Ni or Co with variable metal distribution. Magnetic characteristics like coercivity, magnetic anisotropy and temperature dependent magnetization give a survey about the structure and the magnetic interactions of the nanocomposite. This achieved ferromagnetic nanocomposite system is not only of interest for basic research but also gives rise to applications in magneto-optics, spintronics and sensor application. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Temperature dependence of magnetic microstructure in Fe76Mo8Cu1B15 nanocrystalline alloy

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2004
M. Miglierini
Abstract Fe76Mo8Cu1B15 nanocrystalline alloy featuring close-to-room Curie temperature of 310 K proves to be suitable for model case studies of complexity of magnetic interactions. Annealed samples with different contents of nanocrystallites are characterized by 57Fe transmission Mössbauer spectrometry performed in a wide temperature range (77,673 K). The validity of the temperature dependences of hyperfine parameters is discussed for all structural components including amorphous residual phase, bcc Fe nanocrystals and interface regions located in between the former two. Cautions which must be considered in deriving information about their relative contents are pointed out, because of the presence of static and dynamic effects at high temperatures due to non-interacting and weakly interacting single domain ferromagnetic grains dispersed into a paramagnetic amorphous matrix. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Electronic structure of TbBa2Cu3O7

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2010
Maciej, uszczek
Abstract The full-potential linearized augmented plane wave (FP-LAPW) method was used for spin-polarized electronic structure calculations of stoichiometric TbBa2Cu3O7 (Tb123), not synthesized as a single phase yet. The generalized gradient approximation plus Hubbard correction (GGA,+,U) was employed for Tb4f electrons to prevented fractional occupation of states at Fermi level and hybridization with other electrons. The determined band structure is Y123-like with the metallic character as in the other superconducting R123 (R,=,rare earth). The presented results indicate that strong on-site spin moment of Tb could not effectively influence the neighbours and the induced magnetic interactions in the system are weak (CuO planes) or negligible (BaO planes and CuO chains). This appears to be the repercussion of the ,size effect' due to relatively small Tb+3 ionic radius. The predicted weak influence of magnetic moments of Tb on CuO states in the assumed (hypothetical) Fermi liquid phase of TbBa2Cu3O7 could favour the rise of superconductivity in this system. [source]

Proceedings of the Second Seeheim Conference on Magnetism (SCM2004)

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004
Mohammad Ghafari
The Second Seeheim Conference on Magnetism took place in Seeheim, Germany, 27 June,1 July 2004. SCM2004 focused on latest developments in the field of magnetism of nano-structured materials, surfaces, interfaces and nanoparticles. These novel materials are connected with many aspects of magnetism such as hard and soft magnetic materials, magnetic interactions, magnetization processes, spin dependent transport properties, and applications. [source]

Preface: phys. stat. sol. (c) 1/12

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004
Chair person Mohammad Ghafari
The Second Seeheim Conference on Magnetism (SCM2004) was the second conference in the tri-annual series of this conference series on magnetism, organized under the auspices of Darmstadt University of Technology, Forschungszentrum Karlsruhe and Ulm University. SCM2004 was held from 27 June to 1 July 2004. The location was the Lufthansa Training Center in Seeheim located conveniently in central Germany and easily accessible by air, train and car. The purpose of the meeting was to provide an opportunity to present and discuss recent developments in the field of magnetic nanomaterials. SCM2004 was focused on the latest developments in specific areas of magnetism (nanostructured materials, surfaces, interfaces and nanoparticles) and covered fundamental aspects of magnetism as well as applications. The most recent results were presented in the form of invited and contributed talks as well as posters. The topical areas were: ,,hard and soft magnetic materials ,,magnetic interactions ,,magnetization processes ,,spin dependent transport properties ,,nanostructured materials ,,applications. The first conference of this series was held in Seeheim in 2001. The papers from the 2001 conference were published in a regular issue of physica status solidi (a) 189, Nos. 2, 3 (2002), and since their publication they have been downloaded from the Web more than 14,000 times. This cleary demonstrates both the interest in and the need for this conference series. Our second meeting was attended by participants from 36 countries. A total number of 271 papers correlating nanostructure and magnetic properties were selected for presentation. Throughout the meeting a total of 51 talks was given; the remaining 220 papers were selected for poster presentation. The conference proceeded in an informal and very friendly atmosphere among the researchers from various parts of the world. We are grateful to the Deutsche Forschungsgemeinschaft, Forschungszentrum Karlsruhe and Darmstadt University of Technology for their kind financial support. We are looking forward to welcoming again participants of SCM2004 at the Third Seeheim Conference on Magnetism, planned for 2007 in Seeheim. [source]

Thin films of Co3O4, MnCo2O4 and their solid solution as electrocatalyst: study of their magnetic properties

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2004
E. Ríos
Abstract We present magnetic measurements performed on the MnxCo3,xO4 (0 , x , 1) solid solution, prepared by spray pyrolysis. Thin films of about 20 ,m thickness were obtained after depositing aqueous metal nitrates precursors on Ti or conducting glass substrates. Powder material scratched from the substrate's surface was used for physico-chemical characterization. Presence of two oxidation states for each metal ion (Mn3+,Mn4+; Co2+,Co3+) triggers specific conduction mechanisms and double-exchange magnetic interactions. The ferromagnetic components are enhanced when x(Mn) increases, in detriment of the antiferromagnetic interactions. The ordering temperature Tc changes with x (from 22 K up to room temperature, for x = 0 up to x = 1). Based in the paramagnetic moment ,eff obtained at T > Tc, we propose a cationic distribution which can be nicely compared to the one obtained from crystallographic analyses. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Towards a Better Understanding of Magnetic Interactions within m -Phenylene ,-Nitronyl Nitroxide and Imino Nitroxide Based Radicals, Part III: Magnetic Exchange in a Series of Triradicals and Tetraradicals Based on the Phenyl Acetylene and Biphenyl Coupling Units

A Nonanuclear Copper(II) Polyoxometalate Assembled Around a ,-1,1,1,3,3,3-Azido Ligand and Its Parent Tetranuclear Complex

CHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2005
Pierre Mialane Dr.
Abstract Reaction of CuII, [,-SiW10O36]8,, and N3, affords three azido polyoxotungstate complexes. Two of them have been characterized by single-crystal X-ray diffraction. Complex KNaCs10[{,-SiW10O36Cu2(H2O)(N3)2}2],26,H2O (1) is obtained as crystals in few hours after addition of CsCl. This linear tetranuclear CuII complex consists in two [,-SiW10O36Cu2(H2O)(N3)2]6, units connected through two WO bridges. When the filtrate is left to stand for one night, a new complex is obtained. From both elemental analysis and IR spectroscopy, it has been postulated that this compound could be formulated K1.5Cs5.5[SiW10O37Cu2(H2O)2(N3)],14,H2O (1,a), showing the loss of one azido ligand per polyoxometalate unit. Finally, when no cesium salt is added to the reaction medium, the nonanuclear complex K12Na7[{SiW8O31Cu3(OH)(H2O)2(N3)}3(N3)],24,H2O (2) is obtained after three days. Compound 2 crystallizes in the R3c space group and consists in three {Cu3} units related by a C3 axis passing through the exceptional ,-1,1,1,3,3,3-azido bridging ligand. Each trinuclear CuII unit is embedded in the [,-SiW8O31]10, ligand, an unprecedented tetravacant polyoxometalate, showing that partial decomposition of the [,-SiW10O36]8, precursor occurs with time in such experimental conditions. Magnetically, complex 1 behaves as two isolated {Cu2(,1,1 -N3)2} pairs in which the metal centers are strongly ferromagnetically coupled (J=+224 cm,1, g=2.20), the coupling through the WO bridges being negligible. The magnetic behavior of complex 2 has also been studied. Relatively weak ferromagnetic couplings (J1=+1.0 cm,1, J2= +20.0 cm,1, g=2.17) have been found inside the {Cu3} units, while the intertrimeric magnetic interactions occurring through the hexadentate azido ligand have been found to be antiferromagnetic (J3=,5.4 cm,1) and ferromagnetic (J4=+1.3 cm,1) with respect to the end-to-end and end-on azido-bridged CuII pairs, respectively. [source]