Search results for "spin [structure function]"
showing 10 items of 1132 documents
Muon spin relaxation studies of iron(II) spin crossover complexes
2008
A series of model iron(II) spin crossover complexes have been investigated by temperature dependent muon spin relaxation (mu SR) techniques at ISIS, UK. The thermally induced spin crossover in these materials could be monitored by following the initial asymmetry parameter, a(0), in zero-field. We established that the behavior of a(0) correlates well with the shape of the spin crossover curve derived from magnetic susceptibility measurements, whether hysteretic, smooth, or abrupt. In addition, the longitudinal field dependence of a(0) not only provides information on the nature of the muonic species but also on their interactions and respective localization in the crystal lattice. Useful ins…
Nonlinear dependence on temperature and field of electron spin depolarization in GaAs semiconductors
2009
In this work the influence of temperature and drift conditions on the electron spin relaxation in lightly doped n-type GaAs bulk semiconductors is investigated. The electron transport, including the evolution of the spin polarization vector, is simulated by a Monte Carlo procedure which keeps into account all the possible scattering phenomena of the hot electrons in the medium. Electron-spin states in semiconductor structures relax by scattering with imperfections, other carriers and phonons. Spin relaxation lengths and times are computed through the D'yakonov-Perel process since this is the more relevant spin relaxation mechanism in the regime of interest (10 < T < 300 K). The decay of the…
Doping dependence of spin lifetime of drifting electrons in GaAs bulks
2010
We study the effect of the impurity density on lifetimes and relaxation lengths of electron spins in the presence of a static electric field in a n-type GaAs bulk. The transport of electrons and the spin dynamics are simulated by using a semiclassical Monte Carlo approach, which takes into account the intravalley scattering mechanisms of warm electrons in the semiconductor material. Spin relaxation is considered through the D'yakonov-Perel mechanism, which is the dominant mechanism in III-V semiconductors. The evolution of spin polarization is analyzed by computing the lifetimes and depolarization lengths as a function of the doping density in the range 10^{13} - 10^{16} cm^{-3}, for differ…
Spin forbidden chemical reactions of transition metal compounds. New ideas and new computational challenges.
2003
International audience; Many reactions of transition metal compounds involve a change in spin. These reactions may proceed faster, slower—or at the same rate as—otherwise equivalent processes in which spin is conserved. For example, ligand substitution in [CpMo(Cl)2(PR3)2] is faster than expected, whereas addition of dinitrogen to [Cp*Mo(Cl)(PMe3)2] is slow. Spin-forbidden oxidative addition of ethylene to [Cp*Ir(PMe3)] occurs competitively with ligand association. To explain these observations, we discuss the shape of the different potential energy surfaces (PESs) involved, and the energy of the minimum energy crossing points (MECPs) between them. This computational approach is of great he…
Ligand dissociation accelerated by spin state change: locating the minimum energy crossing point for phosphine exchange in CpMoCl2(PR3)2 complexes
2000
International audience; The minimum energy crossing point between the doublet and quartet potential energy surfaces of CpMoCl2(PH3)2 is calculated to lie 4.8 kcal mol−1 lower in energy than the doublet dissociative intermediate CpMoCl2(PH3). Implications for the influence of spin state changes on the rates of organometallic reactions are discussed.
Single-Molecule-Magnet Fe Fe and Antiferromagnetic Fe Coordination Clusters
2019
Supported by endogenous (part of the ligand, in-built) phenoxo bridges provided by the ligand 2,6-bis[{{(5-bromo-2-hydroxybenzyl)}{(2-(pyridylethyl)}amino}methyl]-4-methylphenol) (H3L), in its deprotonated form, exogenous (not part of the ligand, externally added or generated) oxo-/hydroxo- and acetato-bridged [FeII4FeIII2(O)2(O2CMe)4(L)2]·4Et2O (1) and [FeIII4(OH)2(O2CMe)3(L)2](ClO4)·3MeCN·2H2O (2) coordination clusters have been synthesized and structurally characterized. Complexes 1 and 2 have μ4-O and μ3-OH bridges, respectively. Magnetic studies on 1 reveal slow magnetic relaxation below 2 K. Both in-phase ( χ'M) and out-of-phase (χ″M) magnetic susceptibility were found to be frequency…
Influence of Metal Dilution on the Light‐Induced Spin Transition in Two 1D Chain Compounds: [Fe x Zn 1– x (btzp) 3 ](BF 4 ) 2 and [Fe x Zn 1– x (endi…
2008
The thermal and light-induced spin transitions in [FexZn1–x(btzp)3](BF4)2 and [FexZn1–x(endi)3](BF4)2 {btzp = 1,2-bis(tetrazol-1-yl)propane; endi = 1,2-bis(tetrazol-1-yl)ethane} chain compounds have been investigated by magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. These compounds display a thermal spin transition and the Light-Induced Excited Spin State Trapping (LIESST) effect at low temperature. For each compound, the thermal spin transition temperature, T1/2, and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. A decrease in T1/2 induces an increase in T(LIESST). The results are discussed an…
Solvent-dependent SCO Behavior of Dinuclear Iron(II) Complexes with a 1,3,4-Thiadiazole Bridging Ligand
2016
Two dinuclear iron(II) complexes [Fe2(μ-L)2]X4*4DMF (X = BF4(-) (1·4DMF) and ClO4(-) (2·4DMF)) with a 1,3,4-thiadiazole bridging ligand have been synthesized and show a very distinct solvent-depending SCO behavior. The complexes represent new solvatomorphs of the first dinuclear iron(II) complexes with the ligand L (2,5-bis[(2-pyridylmethyl)amino]methyl-1,3,4-thiadiazole). The incorporated lattice DMF molecules directly affect the spin state of these complexes. This behavior reveals a structural insight into the role of the solvent molecules on the spin transition.
Very Long-Lived Photogenerated High-Spin Phase of a Multistable Spin-Crossover Molecular Material
2018
The spin-crossover compound [Fe(n-Bu-im)3(tren)](PF6)2 shows an unusual long relaxation time of 20 h after light-induced excited spin state trapping when irradiating at 80 K. This is more than 40 times longer than when irradiating at 10 K. Optical absorption spectroscopy, magnetometry, and X-ray diffraction using synchrotron radiation were used to characterize and explain the different relaxation behaviors of this compound after irradiation below and above 70 K. Rearrangement of the butyl chains of the ligands occurring during the relaxation after irradiation above 70 K is thought to be responsible for the unusually long relaxation time at this temperature.
Raman spectroscopy of the high- and low-spin states of the spin crossover complex Fe(phen)2(NCS)2: an initial approach to estimation of vibrational c…
2000
Abstract Raman spectra of the spin-crossover complex Fe(phen)2(NCS)2 in the solid state have been recorded at 785 nm as a function of temperature to investigate the contribution of intramolecular vibrations to the entropy change, ΔS, associated with spin crossover. The modes of major interest for estimating the contribution lie in the range 100–500 cm−1, where the largest qualitative changes with temperature in the Raman spectra were observed. Analysis of these data, with the working assumption of an average frequency in this range as representative of the 15 distortion modes of an idealised FeN6 octahedron, leads to the conclusion that the intramolecular vibrations represent a primary cont…