Hassan Chamati

We investigate the impact of extended inhomogeneities on the dynamics of nonlinear magnetic excitations (solitons) propagating in a single-ion anisotropic Heisenberg spin chain. The extended inhomogeneous domain consists of a set of neighboring spins with disruption of the exchange interaction and/or easy-axis anisotropy. To explore the dynamics of the magnetization, we derive the corresponding Schrödinger equation incorporating linear and nonlinear perturbative terms. While, in the case of a homogeneous chain with an easy-axis anisotropy, the ensuing equation possesses a bright soliton-like solution, an extended inhomogeneity in the spin coupling and/or the anisotropy leads to a physically rich behavior in the soliton dynamics. An inhomogeneous domain with enhanced exchange interaction induces a potential barrier that either transmits or reflects the incident soliton. On the other hand, a segment with reduced coupling brings about a potential well that for a given range of initial velocities and exchange interaction mismatch the scattering patterns exhibits periodic regions of transmissions and trapping as a function of the length of the inhomogeneous domain. The transmission is associated with an excitation and a subsequent resonant de-excitation of the soliton’s shape oscillations at the well boundaries. A thorough analysis shows that the oscillations emanate from the interference of the solitons with emitted spin waves. The interplay of the exchange interaction and single-ion anisotropy mismatch leads to unusual soliton dynamics promoting a complex potential profile in the inhomogeneous domain.

We present a comprehensive review on the major role played by quasiparticles in the advancement of solid state physics with a focus on the elastic and magnetic excitations. The concept of phonons and magnons as quasiparticles is discussed and their relevant parameters including energy spectra are highlighted. The state-of-the-art in molecular and spin dynamics simulations of phonon and magnon spectra in bulk α-Fe by methods, such as the dynamic matrix and dynamic structure factor approach with the aid of different interatomic potentials, is thoroughly analyzed showing their advantages and inconveniences when used to compute the dispersion curves of phonons and magnons and their mutual interaction. This mini review constitutes a pertinent step toward the comprehension of coupled lattice vibrations and magnetic excitations dynamics, and it may stimulate novel research activities in spin transport phenomena.

The major components of cell membranes are phospholipids. Due to their amphiphilic structure, in a solution they arrange in bilayers. The phase behavior of lipid bilayers and thus their functions, such as cellular organization, cellular transport, membrane fusion, drug delivery, and others, are susceptible to temperature changes and/or admixing with biologically active materials. A typical representative of phospholipids is SOPC (1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine) possessing a saturated hydrocarbon acyl chain and an unsaturated one, exhibiting a single cis double bond. Cholesterol plays a primordial role in maintaining the mechanical stability of the cell membrane. We present a comprehensive review of the phase behavior of the binary mixture of SOPC with cholesterol as a function of the temperature explored via atomistic molecular dynamics and Slipids force field in the vicinity of the experimental melting point, Tm = 279 K, corresponding to the temperature driven phase transition from the gel phase (Lβ) to the liquid disordered phase (Lα). The behavior of the thermodynamic properties and structural characteristics with different concentrations of cholesterol show that the pure SOPC bilayer and its counterpart mixed with 10 mol % cholesterol exhibit phase transitions at 277 and 276 K, respectively, and that cholesterol reinforces the fluidity of the bilayer leading to the emergence of a liquid ordered phase (Lo). At cholesterol contents larger than 30 mol %, the bilayer exhibits a liquid ordered phase (Lo) at any temperature. The ensuing phase diagram is found to reproduce reasonably well its counterpart constructed experimentally.

Conducting a thorough theoretical study of the magnetic properties of the spin-one [Ni(Me₆tren)Cl](ClO₄) complex, the present paper unveils the most probable quantum effect underlying the seemingly unusual magnetic behavior of Nickel based complexes exhibiting trigonal (bi-)pyramidal coordination geometry. The study unequivocally shows that the constrained orbital motion of the valence electrons is a primordial quantum effect underlying the rise of a fine structure in the energy spectrum of these molecule magnets and consequently shapes their magnetic behavior. Furthermore, it reveals the ostensible nature of the huge zero-field splitting and points out to the most probable reason to the emergence of such a notion. Accordingly, the probed experimental magnetic properties of the studied complex reported in the literature are reproduced only after the implementation of phase constraints. The conventional approach accounting for the valence electrons as unconstrained does not fit to the experimental findings. The devised method can be applied to study the magnetic properties of all molecule magnets based on metal ions with highly filled valence subshell, including the polynuclear ones.

The typical spectrally limited laser pulse in the near-infrared region is narrow-band up to 40-50 fs. Its spectral width Δk is much smaller than the carrying wavenumber k₀ (Δk ≪ k₀) . For such kinds of pulses, on distances of a few diffraction lengths, the diffraction is of a Fresnel's type and their evolution can be described correctly in the frame of the well-known paraxial evolution equation. The technology established in 1985 of amplification through chirping of laser pulses triggered remarkable progress in laser optics along with the construction of femtosecond (fs) laser facilities producing high intensity fields of the order of 10¹⁵-10²¹ W/cm². However, the duration of the pulse was quickly shortened from picoseconds down to 5-6 fs, which have a broad-band nature (Δk ∼ k₀). The linear and nonlinear propagation dynamics of broad-band pulses is quite different form their narrow-band counterparts. Here, we review the appropriate theoretical approach to study the evolution of the pulse. Moreover, we shed light on the different diffraction regimes inherent to both narrow-band and broad-band laser pulses and compare them to unveil the main differences. Using this very method, in subsequent papers, we will investigate the influence of the dispersion and nonlinearity on the laser pulse propagation in isotropic media.

This paper attempts to shed light on the origin of the magnetic behavior specific to trigonal bi- and pyramidal 3d⁸ mono- and polynuclear nanomagnets. The focus lies on entirely unraveling the system's intrinsic microscopic mechanisms and fundamental quantum mechanical relations governing the underlying electron dynamics. To this end, we develop a self-consistent approach to characterize, in great detail, all electron correlations and the ensuing fine structure of the energy spectra of a broad class of 3d⁸ systems. The mathematical framework is based on the multiconfigurational self-consistent field method and is devised to account for prospective quantum mechanical constraints that may confine the electron orbital dynamics while preserving the properties of all measurable quantities. We successfully characterize the experimentally observed magnetic anisotropy properties of a slightly distorted trigonal bipyramidal Ni²⁺ coordination complex, demonstrating that such compounds do not exhibit intrinsic huge zero-field splitting and inherent giant magnetic anisotropy. We reproduce qualitatively and quantitatively the behavior of the low-field magnetic susceptibility, magnetization, low-, and high-field electron paramagnetic resonance spectroscopy measurements and provide an in-depth analysis of the obtained results.