Search results for "Magnetism"
showing 10 items of 1934 documents
Design of chiral magnets: Cyanide-bridged bimetallic assemblies based on cyclohexane-1,2-diamine
2003
Abstract Four magnetic compounds based on chiral ligands trans-(1S,2S)-chxn and trans-(1R,2R)-chxn (chxn: cyclohexane-1,2-diamine), [Ni(trans-(1S,2S)-chxn)2]3[Fe(CN)6]2·2H2O (1), [Ni(trans-(1R,2R)-chxn)2]3[Fe(CN)6]2·2H2O (2), [Cu(trans-(1S,2S)-chxn)2]3[Fe(CN)6]2·4.5H2O (3) and [Cu(trans-(1R,2R)-chxn)2]3[Fe(CN)6]2·4.5H2O (4), are reported. The four compounds are chiral, as confirmed by X-ray analyses and circular dichroism measurements. From the magnetic point of view, 1 and 2 behave as ferromagnets, whereas 3 and 4 show a paramagnetic behavior.
Unconventional dihydrogen-bond interaction induced cyanide-bridged chiral nano-sized magnetic molecular wheel: synthesis, crystal structure and syste…
2019
A pair of cyanide-bridged 4d–3d heterobimetallic chiral macrocyclic enantiomeric magnetic complexes have been successfully assembled from the trans-dicyanoruthenium(III) building block [PPh4][Ru(Salen)(CN)2] (Salen = N,N-ethylenebis(salicylideneaminato)dianion) and [Mn((S,S/R,R)-Salcy)(H2O)2]ClO4 (Salcy = N,N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato)dianion) with the great help of the dihydrogen bond (DHB) interaction and characterized by elemental analysis, IR spectroscopy, circular dichroism (CD) and magnetic circular dichroism (MCD) spectroscopy. Single X-ray diffraction reveals that complex 1, {[Ru(Salen)(CN)2][R,R-Mn(Salcy)]}6·PPh3·6CH3CN·6CH3OH·12H2O, is a neutral dodecan…
Formation of a novel ferromagnetic end-to-end cyanate bridged homochiral helical copper(ii) Schiff base complex via spontaneous symmetry breaking
2014
A homochiral helical coordination polymer of copper(II) has been synthesized using achiral precursors via spontaneous symmetry breaking and has been confirmed by single crystal X-ray diffraction and solid-state CD spectroscopy. The variable temperature magnetic measurements indicate the presence of weak ferromagnetic exchange interactions mediated by end-to-end cyanate bridges (J = +0.12 cm(-1)).
Dichroism in angular resolved VUV-photoemission from the (0001) surfaces of thin Gd and Nd films epitaxially grown on W(110)
1999
We present investigations of the electronic and magnetic structure of the Rare Earth valence states. In particular, we have examined ultra thin films (≤ 10 ML) of the rare earth metals gadolinium and neodymium epitaxially grown on tungsten (110). Various experiments on dichroism in angular resolved photoemission have been performed using circularly as well as linearly polarised light in the VUV-range with photon energies below 40 eV. A special emphasis was placed on the investigation of the surface state, which was observed for both Gd and Nd. A very small magnetic splitting of about 25 meV was observed for the surface state of ferromagnetic Gd. A magnetic ordering of a Nd-monolayer on a re…
Wedge filling and interface delocalization in finite Ising lattices with antisymmetric surface fields
2003
Theoretical predictions by Parry et al. for wetting phenomena in a wedge geometry are tested by Monte Carlo simulations. Simple cubic $L\ifmmode\times\else\texttimes\fi{}L\ifmmode\times\else\texttimes\fi{}{L}_{y}$ Ising lattices with nearest neighbor ferromagnetic exchange and four free $L\ifmmode\times\else\texttimes\fi{}{L}_{y}$ surfaces, at which antisymmetric surface fields $\ifmmode\pm\else\textpm\fi{}{H}_{s}$ act, are studied for a wide range of linear dimensions $(4l~Ll~320,30l~{L}_{y}l~1000),$ in an attempt to clarify finite size effects on the wedge filling transition in this ``double-wedge'' geometry. Interpreting the Ising model as a lattice gas, the problem is equivalent to a li…
Rigidity transition in two-dimensional random fiber networks
2000
Rigidity percolation is analyzed in two-dimensional random fibrous networks. The model consists of central forces between the adjacent crossing points of the fibers. Two strategies are used to incorporate rigidity: adding extra constraints between second-nearest crossing points with a probability p(sn), and "welding" individual crossing points by adding there four additional constraints with a probability p(weld), and thus fixing the angles between the fibers. These additional constraints will make the model rigid at a critical probability p(sn)=p(sn)(c) and p(weld)=p(weld)(c), respectively. Accurate estimates are given for the transition thresholds and for some of the associated critical e…
Rigidity of random networks of stiff fibers in the low-density limit.
2001
Rigidity percolation is analyzed in two-dimensional random networks of stiff fibers. As fibers are randomly added to the system there exists a density threshold ${q=q}_{\mathrm{min}}$ above which a rigid stress-bearing percolation cluster appears. This threshold is found to be above the connectivity percolation threshold ${q=q}_{c}$ such that ${q}_{\mathrm{min}}=(1.1698\ifmmode\pm\else\textpm\fi{}{0.0004)q}_{c}.$ The transition is found to be continuous, and in the universality class of the two-dimensional central-force rigidity percolation on lattices. At percolation threshold the rigid backbone of the percolating cluster was found to break into rigid clusters, whose number diverges in the…
Rigorous Multimode Equivalent Network Representation of Multilayer Planar Circuits
2018
The objective of this paper is to extend the use of the Multimode Equivalent Network formulation, originally developed to analyze waveguide junctions, to the analysis of planar circuits that include arbitrary rectangular printed, zero thickness metallizations together with internal and external ports in the transverse plane. The theoretical derivations lead to an accurate and computationally efficient tool for the analysis of boxed, multilayer microwave printed circuits. In addition to theory, the tool developed is used here to analyze two practical examples: a dual-bandpass and a 4-pole bandpass boxed microstrip filters. Good agreement with respect to commercial software tools and measurem…
Stability of E' centers induced by 4.7eV laser radiation in SiO2
2007
The kinetics of E' centers (silicon dangling bonds) induced by 4.7eV pulsed laser irradiation in dry fused silica was investigated by in situ optical absorption spectroscopy. The stability of the defects, conditioned by reaction with mobile hydrogen of radiolytic origin, is discussed and compared to results of similar experiments performed on wet fused silica. A portion of E' and hydrogen are most likely generated by laser-induced breaking of Si-H precursors, while an additional fraction of the paramagnetic centers arise from another formation mechanism. Both typologies of E' participate to the reaction with H_2 leading to the post-irradiation decay of the defects. This annealing process is…
Bleaching of optical activity induced by UV Laser exposure in natural silica
2004
We report experimental data on two types of natural silica, differing for their OH content, irradiated with UV photons (4.66 eV) from a pulsed Nd:YAG laser. Irradiation induces a reduction of the absorption band at 5.12eV and of the associated emissions at 3.14eV and 4.28eV, ascribed to twofold coordinated Ge (=Ge'') centers pre-existing in our samples. The bleaching is mainly due to the post-irradiation conversion of =Ge'' into the paramagnetic H(II) center via trapping of a H atom. Comparison with literature data points out the peculiarities of silica with a low Ge concentration as regards UV induced transformations.