Search results for "Magnetism"
showing 10 items of 1934 documents
Thermodynamic properties of a classical d-dimensional spin-S Heisenberg ferromagnet with long-range interactions via the spectral density method
2003
The thermodynamic properties of a classical d-dimensional spin-S Heisenberg ferromagnet, with long-range interactions decaying as $r^{-p}$ and in the presence of an external magnetic field, is investigated by means of the spectral density method in the framework of classical statistical mechanics. We find that long-range order exists at finite temperature for $dd$ with $d>2$, consistently with known theorems. Besides, the related critical temperature is determined and a study of the critical properties is performed.
n-cluster models in a transverse magnetic field
2017
In this paper we analize a family of one dimensional fully analytically solvable models, named the n-cluster models in a transverse magnetic field, in which a many-body cluster interaction competes with a uniform transverse magnetic field. These models, independently by the cluster size n + 2, exibit a quantum phase transition, that separates a paramagnetic phase from a cluster one, that corresponds to a nematic ordered phase or a symmetry-protected topological ordered phase for even or odd n respectively. Due to the symmetries of the spin correlation functions, we prove that these models have no genuine n+2-partite entanglement. On the contrary, a non vanishing concurrence arises between s…
Identification of clusters of companies in stock indices via Potts super-paramagnetic transitions
2000
The clustering of companies within a specific stock market index is studied by means of super-paramagnetic transitions of an appropriate q-state Potts model where the spins correspond to companies and the interactions are functions of the correlation coefficients determined from the time dependence of the companies' individual stock prices. The method is a generalization of the clustering algorithm by Domany et. al. to the case of anti-ferromagnetic interactions corresponding to anti-correlations. For the Dow Jones Industrial Average where no anti-correlations were observed in the investigated time period, the previous results obtained by different tools were well reproduced. For the Standa…
Effect of Cyanato, Azido, Carboxylato, and Carbonato Ligands on the Formation of Cobalt(II) Polyoxometalates: Characterization, Magnetic, and Electro…
2007
Five Co(II) silicotungstate complexes are reported. The centrosymmetric heptanuclear compound K(20)[{(B-beta-SiW(9)O(33)(OH))(beta-SiW(8)O(29)(OH)(2))Co(3)(H(2)O)}(2)Co(H(2)O)(2)]47 H(2)O (1) consists of two {(B-beta-SiW(9)O(33)(OH))(beta-SiW(8)O(29)(OH)(2))Co(3)(H(2)O)} units connected by a {CoO(4)(H(2)O)(2)} group. In the chiral species K(7)[Co(1.5)(H(2)O)(7))][(gamma-SiW(10)O(36))(beta-SiW(8)O(30)(OH))Co(4)(OH)(H(2)O)(7)]36 H(2)O (2), a {gamma-SiW(10)O(36)} and a {beta-SiW(8)O(30)(OH)} unit enclose a mononuclear {CoO(4)(H(2)O)(2)} group and a {Co(3)O(7)(OH)(H(2)O)(5)} fragment. The two trinuclear Co(II) clusters present in 1 enclose a mu(4)-O atom, while in 2 a mu(3)-OH bridging group co…
Synthesis, crystal structure and magnetic properties of [Cu2(bpym)(N3)4] (bpym=2,2′-bipyrimidine)
1993
Abstract The compound of formula [Cu 2 (bpym)(N 3 ) 4 ] (bpym=2,2′-bipyrimidine) has been synthesized and its crystal structure determined by X-ray diffraction methods. It crystallizes in the monoclinic space group P 2 1 / n with cell constants: a =10.071(2), b =6.376(1), c =11.617(2) A and β=95.93(1)°; V =742.0(2) A 3 , D (calc., Z =2)=2.029 g cm −3 , M r =453.4, F (000)=448, λ (Mo Kα)=0.71073 A, μ (Mo Kα)=29.1 cm −1 and T =298 K. A total of 2027 reflections was collected over the range 3⩽2θ⩽55°; of these, 1723 were unique and 1427 were considered as observed ( I >3σ( I )) and used in the structural analysis. The final R and R w residuals were 0.0275 and 0.0328, respectively. The structure…
The Series of Molecular Conductors and Superconductors ET4[AFe(C2O4)3]·PhX (ET = bis(ethylenedithio)tetrathiafulvalene; (C2O4)2– = oxalate; A+ = H3O+…
2011
An extensive series of radical salts formed by the organic donor bis(ethylenedithio)tetrathiafulvalene (ET), the paramagnetic tris(oxalato)ferrate(III) anion [Fe(C(2)O(4))(3)](3-), and halobenzene guest molecules has been synthesized and characterized. The change of the halogen atom in this series has allowed the study of the effect of the size and charge polarization on the crystal structures and physical properties while keeping the geometry of the guest molecule. The general formula of the salts is ET(4)[A(I)Fe(C(2)O(4))(3)]·G with A/G = H(3)O(+)/PhF (1); H(3)O(+)/PhCl (2); H(3)O(+)/PhBr (3), and K(+)/PhI (4), (crystal data at room temperature: (1) monoclinic, space group C2/c with a = 1…
Synthesis, X‐ray Studies and Magnetic Properties of Dinuclear Ni II and Cu II Complexes Bridged by the Azo‐2,2′‐bipyridine Ligand
2003
Two new paramagnetic transition metal complexes that contain the bridging ligand azo-2,2-bipyridine (abpy) have been prepared and characterized by X-ray crystallography and magnetic susceptibility measurements. The compound [Ni2(µ-abpy)(CH3CN)2(NO3)4]·2CH3CN (1·2CH3CN) crystallizes in the triclinic space group P1 ¯ with a = 8.290(5) A u , b = 8.343(5) A u , c = 11.180(5) A u , α = 105.36(3)°, β = 94.39(3)°, γ = 107.56(3)°, V = 700.5(7) A u 3 and Z = 1. The related salt [Cu2(µ
Iron(III), chromium(III) and cobalt(II) complexes with squarate: Synthesis, crystal structure and magnetic properties
2011
The preparation and variable temperature-magnetic investigation of three squarate-containing complexes of formula [Fe 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ]·2H 2 O ( 1 ) [Cr 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ]·2H 2 O ( 2 ) and [Co(C 4 O 4 )(H 2 O) 4 ] n ( 3 ) [H 2 C 4 O 4 = 3.4-dihydroxycyclobutene-1,2-dione (squaric acid)] together with the crystal structures of 1 and 3 are reported. Complex 1 contains discrete centrosymmetric [Fe 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ] diiron(II) units where the iron pairs are joined by a di-μ-hydroxo bridge and two squarate ligands acting as bridging groups through adjacent oxygen atoms. Two coordinated water molecules in cis position complete the octahedral environ…
A Comparative Structural and Magnetic Study of Three Compounds Based on the Cluster Unit M4Cl8(THF)6 (M=Mn, Fe, Co)
2001
Treatment of anhydrous M Cl 2 phases with THF under refluxing conditions leads to excision of the clusters M 4 Cl 8 (THF) 6 ( M =Fe (1), Co (3)) and dimensional reduction to the chain of clusters, {Mn 4 Cl 8 (THF) 6 (Mn(THF) 2 Cl 2 } ∞ , (2). All three compounds were isolated in high yields as crystalline materials and subjected to comprehensive magnetic studies. X-ray structures of the three compounds were performed to verify the nature of the compounds, but only the Mn derivative is discussed in detail due to the fact that the structures of the Fe and Co clusters were reported earlier. The molecular structures of M 4 Cl 8 (THF) 6 ( M =Fe, Co) consist of a rhombic arrrangement of metal ion…
Synthesis, crystal structure and magnetic properties of two alternating double μ1,1 and μ1,3 azido bridged Cu(ii) and Ni(ii) chains
2014
Two new alternating μ1,1- and μ1,3-azido bridged chains, [Cu(N3)2(mtn)]n (1) and [Ni(N3)2(mtn)]n (2) where mtn = N-methyl-1,3-propanediamine, have been synthesized and characterized by single crystal X-ray diffraction. In both complexes, each metal atom is coordinated to six nitrogen atoms from four azide anions and one N-methyl-1,3-propanediamine molecule in a distorted octahedral geometry. In 1, the basal-apical double μ1,1-azido bridged Cu(ii)-dimers are connected through two asymmetric μ1,3-N3 bridges to form a 1D chain in which one of the azide acts as a μ1,1,3 bridge while the other one is terminal. The structure of 2 is very similar but one of the azide ions acts as μ1,1 and the othe…