Search results for "crossover"
showing 10 items of 658 documents
ChemInform Abstract: Spin Crossover, LIESST, and NIESST-Fascinating Electronic Games in Iron Complexes
2010
Abstract Coordination compounds of transition metal ions with open-shell electron configurations may exhibit dynamic electronic structure phenomena depending on the nature of the coordinating ligand sphere. The change of spin state with temperature (thermal spin crossover”) and light-induced electron transfer processes leading to long-lived metastable states are among the most fascinating electronic games encountered in transition metal compounds and are presently under intensive study by chemists and physicists. The first part of this lecture will survey briefly some highlights of previous work and present recent results on thermal spin crossover in iron(II) compounds. The second part of t…
Spin crossover in six-coordinate [Fe(L)2(NCX)2] compounds with L = DPQ = 2,3-bis-(2′-pyridyl)-quinoxaline, ABPT = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4…
1998
[EN] The iron(II) compounds of formulae [Fe(DPQ)2(NCS)2]·CO(CH)3)2(DPQ = 2,3-bis-(2¿-pyridyl)-quinoxaline) (1) and [Fe(ABPT)2-(NCX)2] (ABPT = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) X = S (2) and Se (3) were synthesized and the crystal structure of 1 determined by X-ray diffraction methods. It crystallizes in the monoclinic system . The structure is made up of discrete [Fe(DPQ)2(NCS)2] units. Each metal atom is in a distorted FeN6 octahedral environment, the Fe¿N bonds ranging from 2.013(8) Å to 2.425(8) Å. Variable-temperature magnetic susceptibility data in the temperature range 290¿4.2 K revealed that 1 is high spin, in contrast to 2 and 3 which show a moderately cooperative high s…
Large Conductance Switching in a Single-Molecule Device through Room Temperature Spin-Dependent Transport
2016
Controlling the spin of electrons in nanoscale electronic devices is one of the most promising topics aiming at developing devices with rapid and high density information storage capabilities. The interface magnetism or spinterface resulting from the interaction between a magnetic molecule and a metal surface, or vice versa, has become a key ingredient in creating nanoscale molecular devices with novel functionalities. Here, we present a single-molecule wire that displays large (>10000%) conductance switching by controlling the spin-dependent transport under ambient conditions (room temperature in a liquid cell). The molecular wire is built by trapping individual spin crossover Fe-II comple…
Electric field control of the spin state in mixed-valence magnetic molecules.
2012
Multiferroic molecules for spintronics: In a many-electron mixed-valence dimer with dominant double exchange, as compared with antiferromagnetic superexchange, the electric field is shown to induce a spin crossover from the ferromagnetic spin state to the antiferromagnetic one. This leads to a sharp decrease in the magnetic moment of the molecule and a simultaneous stepwise increase in the electric dipole (see figure).
Critical temperature of the LIESST effect in iron(II) spin crossover compounds
1999
Abstract The light-induced crossover in a series of iron(II) compounds has been investigated by irradiating the sample at 10 K with a Kr + laser coupled to an optical fiber within a SQUID cavity. The temperature dependence of the molar fraction of the light-induced metastable HS state has been recorded for 22 compounds. The critical LIESST temperature, T c (LIESST), has been defined as the temperature for which the light-induced HS information was erased in the SQUID cavity. The dependence of T c (LIESST) as a function of the thermal spin crossover temperature, T 1/2 , has been discussed. The effect of cooperation has been analyzed and the influence of horizontal and vertical displacements …
Nature of crossover from classical to Ising-like critical behavior
1998
We present an accurate numerical determination of the crossover from classical to Ising-like critical behavior upon approach of the critical point in three-dimensional systems. The possibility to vary the Ginzburg number in our simulations allows us to cover the entire crossover region. We employ these results to scrutinize several semi-phenomenological crossover scaling functions that are widely used for the analysis of experimental results. In addition we present strong evidence that the exponent relations do not hold between effective exponents.
Finite-size effects in dynamics of zero-range processes
2010
The finite-size effects prominent in zero-range processes exhibiting a condensation transition are studied by using continuous-time Monte Carlo simulations. We observe that, well above the thermodynamic critical point, both static and dynamic properties display fluid-like behavior up to a density {\rho}c (L), which is the finite-size counterpart of the critical density {\rho}c = {\rho}c (L \rightarrow \infty). We determine this density from the cross-over behavior of the average size of the largest cluster. We then show that several dynamical characteristics undergo a qualitative change at this density. In particular, the size distribution of the largest cluster at the moment of relocation,…
Monte Carlo investigations of phase transitions: status and perspectives
2000
Using the concept of finite-size scaling, Monte Carlo calculations of various models have become a very useful tool for the study of critical phenomena, with the system linear dimension as a variable. As an example, several recent studies of Ising models are discussed, as well as the extension to models of polymer mixtures and solutions. It is shown that using appropriate cluster algorithms, even the scaling functions describing the crossover from the Ising universality class to the mean-field behavior with increasing interaction range can be described. Additionally, the issue of finite-size scaling in Ising models above the marginal dimension (d*=4) is discussed.
High-Temperature Series Analysis of the Free Energy and Susceptibility of the 2D Random-Bond Ising Model
1999
We derive high-temperature series expansions for the free energy and susceptibility of the two-dimensional random-bond Ising model with a symmetric bimodal distribution of two positive coupling strengths J_1 and J_2 and study the influence of the quenched, random bond-disorder on the critical behavior of the model. By analysing the series expansions over a wide range of coupling ratios J_2/J_1, covering the crossover from weak to strong disorder, we obtain for the susceptibility with two different methods compelling evidence for a singularity of the form $\chi \sim t^{-7/4} |\ln t|^{7/8}$, as predicted theoretically by Shalaev, Shankar, and Ludwig. For the specific heat our results are less…
Heavy-tailed targets and (ab)normal asymptotics in diffusive motion
2010
We investigate temporal behavior of probability density functions (pdfs) of paradigmatic jump-type and continuous processes that, under confining regimes, share common heavy-tailed asymptotic (target) pdfs. Namely, we have shown that under suitable confinement conditions, the ordinary Fokker-Planck equation may generate non-Gaussian heavy-tailed pdfs (like e.g. Cauchy or more general L\'evy stable distribution) in its long time asymptotics. For diffusion-type processes, our main focus is on their transient regimes and specifically the crossover features, when initially infinite number of the pdf moments drops down to a few or none at all. The time-dependence of the variance (if in existence…