Mössbauer,magnetic and ir studies of some mononuclear Fe(III) complexes

Mössbauer studies at room temperature and down to liquid nitrogen temperature were supplemented with magnetic and infrared studies of Monochloroferricbis (X-benzoate) and monochloroferricbis (X-chloroacetate). Mössbauer parameters indicate that all the complexes possess high spin configuration in the trivalent and monomeric states. Positive value of V_zz indicates that there is more negative charge in the x-y plane than in along z-axis, suggesting that Fe is penta-coordinated. Molecular weight determination also confirms that the complexes are mononuclear. The effective magnetic moment of the complexes points out to a weak field iron configuration. An attempt has been made to interpret the structure of these complexes on the basis of the measured data.     

Thermal transitions and degradative processes in Fe(III)-tetracarboxyphthalocyanine-grafted poly(N-vinylcarbazole)

The introduction of 2,9,16,23-tetracarboxy-Fe(III)phthalocyanine [Fe(III)tcPc] units onto fractions of poly(N-vinylcarbazole) (PVK) by Friedel-Crafts reaction leads to amorphous PVK-based grafted compounds that show major interchain distances by the wide-angle x-ray scattering (WAXS) technique. Glass transition temperatures of the products are lower than the main glass transition temperature of PVK and are attributed to local movements of the voluminous added groups. Dynamic thermogravimetric experiments show decarboxylation processes within the 250°C-500°C range and little weight loss. The large remaining residue, up to 70% of the sample at 800°C, is suggested to be the consequence of successive cross-linking reactions. The Fourier transform infrared (FTIR) spectrum of the residue is similar to that of the grafted sample before degradation.     

Field-induced magnetic transitions in Pr2(Co,Fe)17

A study of the different magnetic field-induced transitions has been performed for Pr₂Co_17−xFe_x compounds in the temperature range 78–300 K. By using the singular point detection technique, it has been shown that all compounds with x>0 exhibit at least one field-induced transition, which has been identified as a first-order magnetization process (FOMP). Different types of FOMP (A1, A2, P1) are observed, and the change of the type can be induced by varying either temperature or composition. Intermediate Co–Fe compositions show a P1-type FOMP which persists even above room temperature, while a double transition has been found in iron-rich compounds with x⩾13.6. It has also been noticed that, for the particular values of x when a temperature-induced spin reorientation is present, the change from A1 to P1 type FOMP (or vice versa) exactly occurs at the spin reorientation temperature, with a vanishing critical field value. A comparison with the behavior of Y₂Co_17−xFe_x compounds leads to the conclusion that the contributions of the Pr sublattice are essential for the development of these field-induced transitions (some of which are still present at room temperature), even if it is inferred that the overall anisotropy is mainly determined by the 3d sublattice.     

On the behavior of localized magnetic moments in liquid Cu-Al(Fe) alloys

The magnetic properties of dilute Cu-Al alloys with 5 at.% Fe were measured in the solid and liquid states. The results are compared to the Scalapino formula for the susceptibility of dilute alloys. The transition from the magnetic to the non-magnetic state was observed at 41.5 at.% Al.     

Temperature-dependent bandstructure of ferromagnetic metals with localized moments

We consider a theoretical model for ferromagnetic metals like Gd, which takes into account the exchange interaction and the hybridization between two electronic subsystems. The first is built up by quasi-localized electrons, which take care for the existence of permanent magnetic moments, and is described by an atomic limit multiband Hubbard-Hamiltonian. The second subsystem consists of relatively broad conduction bands with more or less free electrons. We investigate the influence of electron correlations on the conduction band states in dependence of temperatureT and bandfillingn. A sensitive reaction of the band states on the magnetic ordering of the moment system leads to strong band deformations. The main goal is the determination of a quasiparticle bandstructure, which we derive in analogy to the experiment (PES, IPE) directly from the spectral density. The new aspect is a splitting of the bare dispersion _m (k) into several quasiparticle dispersion curves with stronglyT-andn-dependent spectral weights. Even forT>T _c an exchange-caused splitting is found. — In this paper we use as input for the free band energies _m (k) a nondegenerate simple cubic-tight binding expression, and in addition seven dispersionlessf-levels, in order to stress mainly the influence of many body effects. It is discussed how the model can be coupled to a LDA bandstructure calculation, in order to get quantitative results for theT-dependent electronic structure of the ferromagnetic 4f-metal Gd, the presentation of which is intended in a forthcoming paper.     

Core polarization corrections to magnetic dipole moments and transitions

Core polarization corrections to ground state magnetic dipole moments are calculated in first-order perturbation theory, with the use of Sussex matrix elements. These corrections are introduced in the particle-(hole-) core coupling model. It is shown that the need for effectiveg _s factors in the calculation of magnetic moments can be explained largely in terms of one-particle-one-hole polarization effects of the core. The influence of these effects on the reducedM1 transition probabilities forl-forbidden transition is also considered.     

A short history of nuclear magnetic moments and GT transitions

We summarize the history and our present understanding of nuclear magnetic moments and Gamow-Teller transitions.The roles of configuration mixing,meson exchange currents and relativistic effects are examined.Experimental evidence for the importance of tensor correlations is also discussed.     

Multiple metamagnetic transitions in the magnetic refrigerant La(Fe,Si)13Hx

The effect of hydrostatic pressure on thermally and field-induced first-order magnetic phase transitions is studied in the La(Fe,Si)_(13)-type compounds. A peculiar series of consecutive field-induced transitions is realized using a distinct combination of hydrostatic pressure and negative pressure created by the interstitial insertion of hydrogen. The pressure-induced discontinuous magnetization jumps result in an enhanced cooling power, thus opening up the possibility to exploit in full the magnetocaloric potential of this compound class.     

过渡金属Mn（Ⅲ）,Fe（Ⅲ）,Rh（Ⅱ）和Pd（Ⅱ）卟啉配合物的共振拉…

讨论了金属离子Ｍｎ（Ⅲ），Ｆｅ（Ⅲ），Ｒｈ（Ⅲ）和Ｐｄ（Ⅱ）原卟啉Ⅸ－二甲酯（ＰＰ）和四苯基卟啉（ＴＰＰ）配合物及Ｐｄ（Ⅱ）间氯四苯基卟啉（ＴＰＰｍ－ｃｌ）配合物的共振拉曼光谱。利用金属离子外层ｄ电子与卟啉环的作用，解释了配合物结构灵敏带的变化规律，同时讨论了不同卟啉及卟啉环上取代基团对结构灵敏带的影响。     

Ground state spin local magnetic moments of deposited Fe clusters

By using the d band model within the Hartree-Fock approximation, we calculate the magnetic ground state of free and deposited Fe_N clusters (N≤30). Fe bcc and Cu fcc (100) monolayers are used as models for the deposition. A comparison between the two kinds of deposition is done. As physically expected, the more is the hybridization of a cluster with the substrate monolayer, the more is the change in its magnetic state when it is deposited. The sites of the cluster, which interact in a collective way with the substrate, are the most susceptible to change their spin local magnetic moments, when the cluster is deposited. In addition, we determined the range of the magnetic interaction of the cluster over the substrate using the obtained results.     

Spin and orbital magnetic moments of Fe3O4

We present measurements of the spin and orbital magnetic moments of Fe3O4 by using SQUID and magnetic circular dichroism in soft x-ray absorption. The measurements show that Fe3O4 has a noninteger spin moment, in contrast to its predicted half-metallic feature. Fe3O4 also exhibits a large unquenched orbital moment. Calculations using the local density approximation including the Hubbard U method and the configuration interaction cluster-model suggest that strong correlations and spin-orbit interaction of the 3d electrons result in the noninteger spin and large orbital moments of Fe3O4.     

Chelate complexes of gold(III)

New gold(III) complexes involving substituted picolinic acids acting as bidentate ligands have been characterised: [AuCl₂(LL), and [Au(LL)₂]⁺ (H-LL=hydroxy- or carboxy-substituted picolinic acid). The latter readily undergo deprotonation of the substituent on one ligand, to yield novel uncharged complexes which appear to be polymeric via hydrogen bonds between protonated and depronated substituents. A completely depronated anionic complex has also been obtained. The characterisation of these materials was considerably aided by¹⁹⁷Au Mussbauer spectroscopy.     

Features of the magnetic and dielectric behavior of mesophases of chromium (III) complexes with azacyclic ligands

Two paramagnetic (1, 2) chromium metallomesogens were studied by the EPR, magnetic-susceptibility, and dielectric-spectroscopy methods. These mesogens possess columnar liquid-crystal phase polymorphism. For mesogen 1 in the columnar Col_xd phase, an irreversible structural phase transition was detected by the EPR method. An anomalous nonlinear temperature dependence of the resonance fields of the EPR line positions and of the fine-structure parameter D in the mesophases of compound 1 was observed. It was shown that this anomaly is associated with the soft mode of crystal lattice. The dielectric spectroscopy data provide support for the existence of the soft mode, which is probably due to the transition of the system from a paraelectric to a dipole-ordered state. The structure of the hexagonal columnar plastic phase of mesogen 2 is formed by a single type of paramagnetic monomer chromium center and does not exhibit any specific features.     

Non-collinear magnetic moments of seven-atom Cr, Mn and Fe clusters

The non-collinearity of magnetic moments of pentagonal bipyramid Cr₇, Mn₇ and Fe₇ clusters is discussed. The magnetic moments are calculated by the discrete variational non-collinear spin-density functional method. For the Cr₇ cluster, a coplanar magnetic arrangement appears at the large interatomic distance. With decreasing the interatomic distance, the coplanar arrangement changes to the parallel arrangement with a small absolute magnetic moment. For the Mn₇ cluster, the magnetic arrangement changes from coplanar to antiparallel with decreasing the interatomic distance. Also for the Fe₇ cluster, some coplanar magnetic moments appear at the interatomic distance of 2.23 ?. In these coplanar magnetic arrangements, the magnetic moment at the basal site of the pentagon rotates with a step of 144 degrees for the Cr₇ clusters and 72 degrees for the Mn₇ and Fe₇ clusters. Received 30 November 2000     

Electrical behavior of poly(N-vinylcarbazole) modified with Fe(III)-phthalocyanine

The grafting reaction of Fe(III)-2,9,16,23-tetracarboxy-phtha-locyanine units onto poly(N-vinylcarbazole) leads to a new polymeric material exhibiting semiconducting behavior. Reaction in di-methylsulfoxide (DMSO) leads to ligand formation; its complex structure contains a radical cation which is accommodated by the phthalocyanine aromatic structure. The basic character of DMSO molecules, behaving as ligand molecules in the complex, is able to modify the paramagnetism of the central metal ion. By submitting the product to a dc electric field, both electronic and polar contributions to bulk conductivity were found. Measurements in alternating current provide useful information about the inductive, resistive, and capacitive behavior. The values of ac conductivity and loss tangent (tan Θ) are interpreted in terms of the polymer structure.