Physica B+C最新文献

Details of a rigorous least-squares (LSF) procedure for the evaluation of the components of non-coincident tensors $\text{g}{}^2$, $\text{A}{}^2$, $\text{D}$, $\text{P}$ and $\text{g}{}_{\mathrm{n}}{}^2$ using eigenvalues calculated tt second-order in perturbation for electron-nuclear spin-coupled systems are given. The complexities associated with the presence of non-coincident tensors in the spin Hamiltonian are discussed. Details are provided of how the components of the various tensors can be evaluated by choosing either special, or arbitrary, coordinate axes for their descriptions. The procedure is illustrated by application to the X-band EPR data obtained at room temperature for VO²⁺-doped K₂C₂O₄·H₂O single crystal. It is found that, for this case, the LSF procedure, based on the use of second-order eigenvalues, as described here, yields the χ² value, representing the goodness of fit, one-fortieth that found employing the LSF procedure, based on the use of first-order eigenvalues.

We consider a body-centered orthorhombic lattice of reorientable point dipoles which interact with each other electrostatically. The lattice constants are those of NaNO₂, and the dipoles are able to reorient in the bc plane. Using a classical statistical mechanical formalism we find that when the temperature is increased from zero the system undergoes two phase transitions: the first from the ferroelectric to a modulated phase, and the second from the modulated to the totally disordered (paraelectric) phase. The mechanism giving rise to the ferroelectric-modulated phase transition can be described saying that in an intermediate temperature range a state where the entropy is distributed among the dipoles in a modulated way has less free energy than that where all the dipoles are equally disordered.

A certain class of kinks responsible for the proton transport in hydrogen-bonded solids is studied. It is shown that their energies are close to those of ionic defects and of transduction for ATP formation. These kinks are obtained as exact solutions of the equation of motion for the protonic dynamics in the case of one-dimensional chains of hydrogen bonds. The stability of kinks is proved.

The level scheme of trebly ionized thorium atoms is extended and the ionization limit is determined at 231 065 cm⁻¹ (Ky), corresponding to an ionization potential of 28.65 V, with an uncertainty of ±0.03 V. The Stark shifts of low levels in both Th IV and Th III are shown to be connected with the extreme sensitivity of the 5f-orbital to external electric fields, owing to the peculiar shape of the natural effective potential.

Two-sublattice collinear Heisenberg-Ising (S=1) metamagnets with uniaxial four-ion anisotropy are investigated by the high-density expansion method. Formulas in approximation including Gaussian fluctuations of the molecular field for magnetization and free energy are obtained. The magnon frequencies are obtained in approximation including free magnons in the molecular field fluctuating in a Gaussian way. The theoretical results fitted for the FeCl₂ metamagnet yield phase diagram and magnon frequencies in better agreement with the experimental results than other existing theories.

The effect of collective electron oscillations at the surface of the metal compounds has been discussed in the X-ray absorption spectra of several metal compounds. The effect of double plasmon oscillations has also been discussed on the X-ray K or L-absorption edges. As a result of our work, various unexplained chemical shifts have been explained.

The characteristics of a gaseous discharge have been studied in the presence of a localised transverse magnetic field applied to a discharge tube. The breakdown voltage and the post breakdown discharge current are found to be dependent on the strength and the position of the applied magnetic field. The position of the magnetic field at which the electrical parameters of the gaseous discharge are more sensitive to the magnetic field has been identified to be very near the cathode end of the negative glow. All the experimental observations in this study have been explained consistently taking into consideration the complexity of the electrical conduction in the presence of the localised magnetic field.

A mathematical description of axi-symmetrical bubbles as well as experimental results related to their behaviour at low pressures is presented. It is suggested that in vacuum the film forming the bubble changes into a quasi-membrane.