Search results for "transition"
showing 10 items of 3988 documents
First principles simulations of 2D Cu superlattices on the MgO(0 0 1) surface
2004
AbstractFirst principles slab simulations of copper 2D superlattices of different densities on the perfect MgO(001) surface are performed using the DFT method as implemented into the CRYSTAL98 computer code. In order to clarify the nature of interfacial bonding, we consider regular 1/4, 1/2 and 1 monolayer (ML) coverages and compare results of our calculations with various experimental and theoretical data. Our general conclusion is that the physical adhesion associated with a Cu polarization and charge redistribution gives the predominant contribution to the bonding of the regular Cu 2D layer on the MgO(001) surface.
Magnetic and Electronic Properties ofRENiBi (RE = Pr, Sm, Gd-Tm, Lu) Compounds
2008
Resistivity and magnetic measurements were used to examine the ternary rare earth compounds RENiBi (RE = Pr, Sm, Gd-Tm, Lu). These compounds order antiferromagnetically with TN below 16 K (RE = Pr, Sm, Gd-Tm) or are paramagnetic (LuNiBi). For some of these compounds a metal–insulator transition was found. The metal–insulator transition temperature depends strongly on the preparation conditions. Both the magnetic ground states and the resistance behavior are in good agreement with electronic band structure calculations.
Spin transition in [Fe(phen)2(NCS)2] - �SR study
2004
The reversible thermal spin transition which occurs in [Fe(phen)(2)(NCS)(2)] around T-1/2 similar to 177 K has been investigated by muon spin relaxation (muSR) (similar to10-280 K). The depolarisation curves are well described by two Lorentzian lines represent fast and slow components in the decay curves, with the initial asymmetry parameter of the fast component found to track the spin transition in [Fe(phen)2(NCS),]. Comparison of zero-field and transverse field (20 Oe) muSR measurements shows that diamagnetic muonic species occur over the entire temperature range.
Monte Carlo study of cluster-diameter distribution: An observable to estimate correlation lengths
1997
We report numerical simulations of two-dimensional $q$-state Potts models with emphasis on a new quantity for the computation of spatial correlation lengths. This quantity is the cluster-diameter distribution function $G_{diam}(x)$, which measures the distribution of the diameter of stochastically defined cluster. Theoretically it is predicted to fall off exponentially for large diameter $x$, $G_{diam} \propto \exp(-x/\xi)$, where $\xi$ is the correlation length as usually defined through the large-distance behavior of two-point correlation functions. The results of our extensive Monte Carlo study in the disordered phase of the models with $q=10$, 15, and $20$ on large square lattices of si…
Quantum Monte Carlo study of insulating state in NaV2O5
2003
Abstract Quantum Monte Carlo (QMC) methods are being increasingly used as complements to Hartree–Fock (HF) methods for computing the electronic structure of molecules and materials. We investigate the nature of the insulating state driven by electronic correlations in the ladder compound NaV 2 O 5 ; considered as a quarter-filled system. We use an extended Hubbard model (EHM) to study the role of on-site and inter-site Coulomb interaction. It is found that the insulating state in the charge-disordered phase of this compound take origin from the transfer of spectral density and dynamical fluctuations. Our calculation allows us also, to understand the origin of the insulating states above T C…
Neutron diffraction studies of the molecular compound [Co 2(bta)]n (H4bta =1,2,4,5-benzenetetracarboxylic acid): In the quest of canted ferromagnetism
2013
The exchange mechanism and magnetic structure of the organic-inorganic layered molecule-based magnet [Co2(bta)]n (1) (H 4bta =1,2,4,5-benzenetetracarboxylic acid) have been investigated through variable-temperature magnetic susceptibility measurements and supported with a series of neutron diffraction experiments. Cryomagnetic studies have shown an antiferromagnetic ordering at a transition temperature of 16 K that is followed by the appearance of a weak ferromagnetism below 11 K. The weak antiferromagnetic interlayer interaction plays an important role in this system in spite of the long interlayer separation. A ferromagnetic ordering is induced by applied magnetic fields greater than 1800…
Debye-Waller factor in the spin crossover complex Fe(ppi)2(NCS)2
1997
Abstract Mossbauer spectroscopy and magnetic susceptibility measurements for the complex Fe(ppi) 2 (NCS) 2 in the temperature range 11–300 K indicate that the spin transition of this compound is incomplete until 11 K. The similar Debye-Waller factors in high spin (HS) and low spin (LS) states is shown by the comparison of the HS fractions from the two different methods. The Debye temperature of the compound was calculated from the defined Debye-Waller factors obtained from Mossbauer measurement at each experimental temperature and was found to depend on the temperature as well as on the HS fraction. The modification of the Debye-Waller factors in the HS and LS states for the HS fraction fro…
Monte Carlo Study of Dense Monolayer and Bilayer Films on the (100) Plane of Face-Centered Cubic Crystals
1999
A Monte Carlo simulation method in the canonical and in the grand canonical ensembles is used to study the behavior and properties of dense monolayer and bilayer films formed on the (100) plane of model face-centered cubic crystals. Systems with different effects due to the periodicity of the gas−solid potential are considered, and the mechanism of melting in the first and the second adsorbed layer is discussed. It is demonstrated that the film structure is very sensitive to the gas−solid potential corrugation, as well as to the temperature and the surface coverage. In particular, it is shown that monolayer films formed on weakly corrugated surfaces exhibit the incommensurate (dense) phase …
Pressure Effect on Spin Crossover in [Fe(phen)2(NCS)2] and [CrI2(depe)2]
2004
In the present article, we discuss the results of investigations of the influence of hydrostatic pressure (up to 1.2 GPa) on the spin transition behavior in [Fe(phen)2(NCS)2] polymorph II and [CrI2(depe)2]. It is demonstrated that pressure effect studies are very helpful in elucidating the mechanism of cooperative dynamic electronic structure phenomena accompanied by significant volume changes. Application of hydrostatic pressure serves as a tool for modifying the ligand field strength in a controlled manner.
Spin-polarization effects for electrons passing through thin iron and cobalt films
1993
Abstract Spin-dependent effects of the inelastic mean free path (IMFP) are evident for low-energy electrons passing through magnetized ferromagnetic films caused by a different attenuation within the layer. Values of IMFP for both spin components were determined for ultrathin iron and cobalt layers on W(1 1 0) by means of spin-resolving photoelectron spectroscopy.