A. Caillé

Asymmetrical guided magnetic polaritons in a ferromagnetic slab

Abstract The dispersion relations for guided magnetic polaritons are obtained in an ordered ferromagnetic slab. For this anisotropic system, the guided modes do not have the reflection symmetry with respect to the median plane of the slab which is known to exist for the dielectric polaritons in an ionic crystal slab. The dispersion relations and the phase angles are given for typical values of the parameters.

An Ising-like model of stacking-sequence polytypism in ABX3 compounds

The crystallographic structure of a large class of ABX3 compounds can be characterised by the stacking sequences of face- and corner-sharing BX6-octahedra chains on a hexagonal lattice. Many different polytypes described by this type of stacking have been observed in these and related materials. An axial Ising-type model free energy that includes terms linear and cubic in the pseudo-spin variable is proposed to describe the possible phases which result from interactions between octahedra. The model is also shown to account for the increase in corner-sharing sequences with increasing pressure observed in, for example, CsBF3B=Mn, Fe, Co, Ni.

Surface magnetic polaritons on uniaxial antiferromagnets

Abstract The dispersion relation of surface polaritons for a uniaxial antiferromagnet are calculated taking account of retardation. In the presence of an external magnetic field, one finds that inequivalent propagation occurs in the Voigt configuration (± n × H 0 ). For a high frequency permeability smaller than a critical value, the surface polaritons in the − n × H 0 direction, where n is the normal to the interface, merges in the same frequency domain as the bulk polaritons.

First order spin–Peierls transition in a quantum antiferromagnetic Heisenberg chain

The problem of the linear antiferromagnetic Heisenberg chain of elastically coupled spins is investigated in the Hartree–Fock approximation and using mean field theory. At low temperature this system undergoes a phase transition, called spin–Peierls, to a dimerized state. Using an exponential variation of the exchange parameters with the distance between the ions, we show that the transition is of first order for any value of interest of the parameters in the theory. Previous results, using the linear dependence of the exchange parameters, gave a second order transition. The absence of the second order phase transition is attributed to a pseudofermion–pseudofermion interaction in our calculation.

Histogram Monte Carlo study of the next-nearest-neighbor Ising antiferromagnet on a stacked triangular lattice.

Critical properties of the Ising model on a stacked triangular lattice, with antiferromagnetic first and second-neighbor in-plane interactions, are studied by extensive histogram Monte Carlo simulations. The results, in conjunction with the recently determined phase diagram, strongly suggest that the transition from the period-3 ordered state to the paramagnetic phase remains in the xy universality class. This conclusion is in contrast with a previous suggestion of mean-field tricritical behavior.

Magnetic phase diagrams of spin‐frustrated stacked triangular antiferromagnets: Application to ABX3 compounds (invited)

A review is given of our recent results on magnetically ordered states occuring in geometrically frustrated stacked triangular (simple hexagonal) antiferromagnets based on phenomenological Landau theory, molecular field theory, and Monte Carlo simulations. Novel multicritical behavior in magnetic field‐temperature phase diagrams is demonstrated for systems with axial and planar anisotropy (weak and strong). Crossover effects are discussed in terms of the new chiral universality classes recently proposed by Kawamura. Comparison of theory and simulation results with the observed magnetic ordering and phase diagrams in a wide variety of ABX3 compounds is made.

The interaction of the two-dimensional plasmon with the surface plasmons in an MOS structure

Abstract The two-dimensional electron gas in the inversion layer of an MOS structure gives rise to a two-dimensional plasmon, which has not yet been observed. The interaction of this collective oscillation with the surface plasmons of the semi-metallic film in an MOS structure is calculated in the long wavelength limit. The results indicate large coupling with the tangential surface plasmon and suggest an indirect means of observing the two-dimensional plasmon.

Interaction of interface plasmons and longitudinal optical phonons in a multilayer structure

Abstract The interaction between two-dimensional interface plasmons and longitudinal optical phonons in multilayer structures is analysed in this communication. The dispersion relations for the mixed modes are obtained for periodic boundary conditions in the direction normal to the layer planes. The energy gap between the two bands of mixed modes can be seen in the density of states ϱ k (ω) at fixed k parallel to the layers. ϱ k (ω) also exhibits singularities at the band edges characteristics of the one-dimensional periodic array of parallel layers.

A percolation model for lateral diffusion in cholesterol-phospholipid mixtures

Abstract A simple path model is developed for the lateral diffusion in a cholesterol-phospholipid monolayer. The diffusion constant jumps, as seen by photobleaching recovery near 20%mol cholesterol on both sides of the chain melting transition, is then explained by a two-dimensional percolation argument.

Thermal phase diagrams of columnar liquid crystals

In order to understand the possible sequence of transitions from the disordered columnar phase to the helical phase in hexa(hexylthio)triphenylene (HHTT), we study a three-dimensional planar model with octupolar interactions inscribed on a triangular lattice of columns. We obtain thermal phase diagrams using a mean-field approximation and Monte Carlo simulations. These two approaches give similar results, namely, in the quasi one-dimensional regime, as the temperature is lowered, the columns order with a linear polarization, whereas helical phases develop at lower temperatures. The helicity patterns of the helical phases are determined by the exact nature of the frustration in the system, itself related to the octupolar nature of the molecules.