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51.
J. Linares H. Spiering F. Varret 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):271-275
It is well-known that 1D systems with only nearest neighbour interaction exhibit no phase transition. It is shown that the
presence of a small long range interaction treated by the mean field approximation in addition to strong nearest neighbour
interaction gives rise to hysteresis curves of large width. This situation is believed to exist in spin crossover systems
where by the deformation of the spin changing molecules, an elastic coupling leads to a long range interaction, and strong
bonding between the molecules in a chain compound leads to large values for nearest neighbour interaction constants. For this
interaction scheme an analytical solution has been derived and the interplay between these two types of interaction is discussed
on the basis of experimental data of the chain compound which exhibits a very large hysteresis of 50 K above RT at 370 K. The width and shape of the hysteresis loop depend on the
balance between long and short range interaction. For short range interaction energies much larger than the transition temperature
the hysteresis width is determined by the long range interaction alone.
Received 26 November 1998 相似文献
52.
T. Becze-Deák L. Bottyán D.L. Nagy U.W. Pohl H. Spiering 《Hyperfine Interactions》2000,126(1-4):115-119
Mössbauer emission spectra of a 57Co:ZnSe powder source at low temperature exhibit the overcompensated Fe1+ state of the nucleogenic daughter ion generated as an after effect of the 57Co(EC)57Fe decay. We analyse to what extent the model of competing acceptors is able to account for the formation and fraction of Fe1+ and present evidence for the role of hole trapping by zinc vacancies. 相似文献
53.
Ronayne KL Paulsen H Höfer A Dennis AC Wolny JA Chumakov AI Schünemann V Winkler H Spiering H Bousseksou A Gütlich P Trautwein AX McGarvey JJ 《Physical chemistry chemical physics : PCCP》2006,8(40):4685-4693
The vibrational modes of the low-spin and high-spin isomers of the spin crossover complex [Fe(phen)(2)(NCS)(2)] (phen = 1,10-phenanthroline) have been measured by IR and Raman spectroscopy and by nuclear inelastic scattering. The vibrational frequencies and normal modes and the IR and Raman intensities have been calculated by density functional methods. The vibrational entropy difference between the two isomers, DeltaS(vib), which is--together with the electronic entropy difference DeltaS(el)--the driving force for the spin-transition, has been determined from the measured and from the calculated frequencies. The calculated difference (DeltaS(vib) = 57-70 J mol(-1) K(-1), depending on the method) is in qualitative agreement with experimental values (20-36 J mol(-1) K(-1)). Only the low energy vibrational modes (20% of the 147 modes of the free molecule) contribute to the entropy difference and about three quarters of the vibrational entropy difference are due to the 15 modes of the central FeN(6) octahedron. 相似文献
54.
The Monte Carlo method has been applied to reproduce the two-step spin transition in [FexZn1?x(2-pic)3]Cl2 · EtOH (2-pic = 2-picolylamine). The partition function of the Hamiltonian has been factorized in two parts describing the inner degrees of freedom of the spin transition molecules and the interaction between them. The factorization is equivalent to an effective Hamiltonian which can be mapped on an Ising system in an applied magnetic field. The interaction consists of an infinite range and a short range interaction part. Qualitatively the two-step transition under pressure and the Zn diluted system have been well reproduced with infinite range and the next nearest neighbour interaction of ferromagnetic type and the nearest neighbour interaction of antiferromagnetic type in a simple cubic lattice. 相似文献
55.
A photoelastic and a numerical investigation has been carried out to determine the stress-concentration factors at the edge of a central circular hole in a tensile strip for different ratios of hole diameter to width of the strip. The photoelastic data and the numerical results indicate that the stress-concentration factor at the minimum cross-sectional area tends to a value of two if the ratio of the hole diameter to the strip-width approaches a value of one. 相似文献
56.
57.
Controlled Formation of Patchy Anisometric Fumed Silica Supraparticles in Droplets on Bent Superhydrophobic Surfaces
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Marcel Sperling Vivian J. Spiering Orlin D. Velev Michael Gradzielski 《Particle & Particle Systems Characterization》2017,34(1)
This article presents a study on the formation of anisometric, ellipsoidal supraparticles by evaporation‐induced self‐assembly from multicomponent colloidal dispersion droplets deposited on a superhydrophobic surface. Performing the formation process on bent surface substrates grants precise control on the shape and spatial orientation of the final dried supraparticles. Due to the V‐shaped surfaces providing interfacial blockage, anisotropic evaporation rates occur with respect to the direction of the bending channel. This proportionally leads to inhomogeneous accumulation of fumed silica (FS), used as structure guiding component. Thus, upon the increase of FS‐particle interaction via ionic strength (NaCl), this so‐formed shell provides enough anisotropic stiffness resulting in predictable droplet deformation with the elongation orientation being perpendicular to the bending axis. The anisotropic evaporation rates were monitored and quantified using an established, empiric kinetic model and taking into account surface geometry. Employing this reliable control of elongation direction and using additional Fe3O4@SiO2 core–shell nanoparticles, anisometric magnetic Janus supraparticles with defined patch position were prepared, which are not accessible on flat surfaces. The results can find application in the controlled, easy to scale up, nanofabrication process of patchy anisometric supraparticles. 相似文献
58.
59.
In57Fe Mössbauer emission spectroscopy, the parent nucleus57Co is incorporated in the matrix by diffusion, implantation or co-precipitation. Mössbauer emisssion spectra often differ from the corresponding absorption spectra in several aspects. The “anomalous” features (denoted as “after-effects” of nuclear transformation) comprise mainly (a) anomalous charge states, (b) anomalous spin states, and (c) metastable electronic populations within these charge states. The first two classes of effects were extensively studied during the sixties and seventies. More recently, several investigations have shown that, under certain circumstances, the electronic systems of Fe(II) and Fe(III) have not reached the thermal equilibrium within the Mössbauer time window. These effects have been evidenced (i) within the crystal field ground-state manifolds, but also (ii) as spectral contributions from excited crystal field states. In the present paper, an overview of these experiments will be given, together with their theoretical interpretation and in comparison to results obtained with other methods (e.g. optical spectroscopy). Special emphasis will be given to the systems57Co/LiNbO3 and57Co/MgO, where nonequilibrium populations within the6A1 ground manifold of Fe(III) and Γ5g ground manifold of Fe(II) have been observed in an external magnetic field. 相似文献
60.
Adler Peter Hauser Andreas Vef Andreas Spiering Hartmut Gütlich Philipp 《Hyperfine Interactions》1989,47(1-4):343-356
Hyperfine Interactions - High spin (HS) ⇌ low spin (LS) conversions in transition metal complexes are nonradiative transitions between spin states. In this contribution, we present a study of... 相似文献