Search results for "SPIN STATES"
showing 10 items of 253 documents
A novel paramagnetic molecular superconductor formed by bis(ethylenedithio)tetrathiafulvalene, tris(oxalato)ferrate(iii) anions and bromobenzene as g…
2005
The new paramagnetic molecular superconductor ET4[(H3O)Fe(C2O4)3]·C6H5Br (1) (Tc = 4.0 K) contains layers of superconducting ET donors alternating with paramagnetic hexagonal layers formed by (H3O)+, [Fe(C2O4)3]3− and guest C6H5Br molecules located in the hexagonal cavities. Conductivity measurements show metallic behavior from room temperature with a minimum in the resistivity at ca. 50 K followed by a smooth increase and a sharp drop in the resistivity with an onset at 4.0 K and a zero resistance at ca. 1.0 K. Magnetoresistance measurements indicate that Hc1 is about 7 mT and that Hc2 is very anisotropic (Hc2⊥ ≥ 5.5 T and Hc2|| ≈ 0.5 T). Magnetic susceptibility measurements show the expec…
Transport anisotropy and of thin films
2005
Abstract The resistivity R ( T ) of superconducting UNi 2 Al 3 thin films shows a pronounced dependence on the current direction. Specifically, the superconducting transition temperature T c is directional dependent as well as the influence of the magnetic ordering on the transport properties. Also the upper critical field B c 2 ( Θ , T ) is moderately influenced by the probe current direction. These anisotropies are discussed in the framework of multiband superconductivity. The initial slope of the upper critical field B c 2 ′ ( T ) provides evidence for a spin singlet state.
A penetration depth study on the non-centrosymmetric superconductors Li2(Pd1−xPtx)3B
2008
Abstract We study the superconducting order parameter in the non-centrosymmetric compounds Li 2 (Pd 1− x Pt x ) 3 B ( x =0, 0.3, 0.7 and 1) by measuring magnetic penetration depth λ ( T ). The low temperature λ ( T ) shows a linear temperature dependence for x ⩾0.3, but follows exponential-like behavior for lower Pt contents. These findings suggest that a spin-triplet state might gradually develop with increasing x due to the broken inversion symmetry.
Cooperative Thermal and Optical Switching of Spin States in a New Two-Dimensional Coordination Polymer
2003
{Fe(pmd)2[Cu(CN)2]2} (pmd = pyrimidine) displays a rigid two-dimensional structure and undergoes thermal- and optical-driven spin crossover behaviour; cooperative elastic coupling between iron(II) ions in the framework induces thermal hysteresis in the HS↔LS conversion and sigmoidal HS→LS relaxation of the photo-induced HS state at low temperatures. Niel, Virginie, Virginie.Niel@uv.es ; Galet Domingo, Ana Guadalupe, Ana.Galet@uv.es ; Gaspar Pedros, Ana Belen, Ana.B.Gaspar@uv.es ; Real Cabezos, Jose Antonio, Jose.A.Real@uv.es
catena-[µ-Tris(1,2-bis(tetrazol-1-yl)ethane-N4,N4')iron(II)] bis(tetrafluoroborate): synthesis, structure, spectroscopic and magnetic characterizatio…
2002
In analogy to a common synthesis of 1-substituted 5-H tetrazoles (Tetrahedron Lett. 36 (1995)1759; Beloruss. Gos. Univ., Minsk, USSR. Khim. Geterotsikl. Soedin. 11 (1985) 1521; Beloruss. Gos. Univ., Minsk, USSR. Khim. Geterotsikl. Soedin. 1 (1991) 66; BGU, Belarus. Vestsi Akad. Navuk Belarusi, Ser. Khim. Navuk 1 (1992) 73), the new bidentate ligand 1,2-bis(tetrazol-1-yl)ethane [endi] was synthesized and characterized by X-ray diffraction, NMR, IR and UV–Vis spectroscopy. By using iron(II) tetrafluoroborate hexahydrate the complexation with this ligand yields a 1-dimensional linear coordination polymer similar to the recently published chain compound (Inorg. Chem. 39 (2000) 1891) exhibiting …
The Two‐Step Spin Conversion in a Supramolecular Triple Helicate Dinuclear Iron(II) Complex Studied by Mössbauer Spectroscopy
2006
The triple helicate dinuclear iron(II) complex, [Fe-2(L)(3)](ClO4)(4)center dot 2H(2)O (1), previously reported by Tuna et al. (Chem. Eur. J. 2004, 10, 5737), was prepared and characterised by detailed SQUID and Fe-57 Mbssbauer measurements. Compound 1 exhibits a thermochromic two-step spin conversion at T-SC((1)) ca. 240 K and T-SC((2)) ca. 120 K, but does not switch its spin state further below 20 K as proven by Mossbauer spectroscopy. The sharp variation of the susceptibility below 20 K is due to zero-field splitting of the remaining iron(II) high-spin species. Applied field Fe-57 Mossbauer spectroscopy experiments at 4.2 K indicate that the gradual thermal spin conversion from [HS-HS] p…
Thermal and Light-Induced Spin Transition in [Fe(bpen)X2] (bpen = 1,6-Bis(2-pyridyl)-2,5-diazahexane, X = NCS-, NCSe-)
1996
The thermal and light-induced spin transitions in [Fe(bpen)(NCS)2] and [Fe(bpen)(NCSe)2] have been investigated by means of magnetic susceptibility and Mossbauer measurements. The HS → LS transition in [Fe(bpen)(NCS)2] is detected at temperatures below 120 K (T1/2 [when the fraction of high-spin species γHS = 0.5] = 68 K) with a residual HS fraction of 8% at 20 K. The transition is fairly abrupt and no hysteresis is observed, in contrast to earlier studies (ref. [8]). The generation of metastable HS states in [Fe(bpen)(NCS)2] is achieved by rapid cooling of the sample and by irradiating the compound at low temperatures with light of appropriate wavelengths (LIESST). The HS → LS relaxation o…
Magnetic mixed-valence d2-d1-d1 trimers with partial electron delocalization: vibronic coupling and magnetic properties
1993
Abstract The energy levels and magnetic properties of a triangular mixed-valence cluster d1-d1-d2 with electron delocalization in a pair of sites are examined from a model that takes into account electron transfer, magnetic exchange, and vibronic coupling. We show that the electron transfer process involves besides the usual double-exchange parameter, and additional parameter referred to as exchange transfer. This last parameter accounts for the interaction between the moving electron of the mixed valence pair and the electron localized in the third side. We notice that the role of double exchange is to stabilize a ferromagnetic alignment of the spins on the mixed-valence pair. A comparison…
Electric field control of the optical properties in magnetic mixed-valence molecules
2014
We propose the use of an electric field stimulus to strongly affect the optical properties of ferromagnetic mixed-valence (MV) dimers. This proposal is based on the prediction of an anomalous Stark effect in the intervalence absorption bands of these multi-electron MV systems. As distinguished from the conventional Stark effect observed in one-electron dimers, a strong change of the intervalence bands accompanies the crossing of the different spin levels caused by the application of an electric field. This new effect can be referred to as giant spin-dependent Stark effect. In spintronics this opens up the possibility for optical detection of the spin state in these magnetic molecules.
Mixed-valence polyoxometalate clusters. I. Delocalization of electronic pairs in dodecanuclear heteropoly blues with keggin structure
1995
Abstract The problem of delocalization of a pair of electrons over dodecanuclear polyoxometalate clusters with the Keggin structure is considered with the aim of explaining the spin pairing in these multi-nuclear mixed-valence systems. A general approach that considers the Coulomb interactions between the two delocalized electrons, as well as the single and double electron transfer processes which can be operative in delocalization of the electronic pairs is developed. The new approach is based on the site-symmetry concept which makes possible a group theoretical classification for the delocalized states of electronic pairs. This procedure proves to be very efficient in the calculation of t…