Vibronic structure and the anisotropy of excitons in cubic LiH single crystals

The shape of one-phonon sidebands of exciton in LiH is studied both in reflection and edge luminescence spectra. The main structure of the shape is found to reflect the phonon density of states. This fact is interpreted as a result of a high anisotropy of the exciton band.     

Sound velocity anisotropy in cubic crystals

Simple analytical expressions may be derived for sound velocities in cubic crystals by using lattice harmonics or functions which are invariant under the crystal symmetry operations. These expressions are in good agreement with the exact results for typical crystals such as metallic iron and potassium fluoride.     

Coupled m-component fields with cubic anisotropy

The critical behavior at phase transitions of two coupled, m-component systems with cubic anisotropy is studied by a simplified model in which the fluctuations are partially considered. The phase transition could be a new fluctuation-induced first order transition into the anisotropic phase, or a new second order phase transition. Unlike in uncoupled systems, the second order phase transition could be into either the anisotropic or isotropic phase. As expected, upon suppression of fluctuations, all results reduce to those of mean field theory.     

Frustrated antiferromagnetic spin 1 Heisenberg model with single ion anisotropy on a simple cubic lattice

We study the effects of frustration between nearest, next-nearest neighbor and next-next-nearest neighbors (NNN) of the quantum S=1 anisotropic antiferromagnetic Heisenberg model on a simple cubic lattice with single ion anisotropy using the bond operator technique. We calculate the phase diagram at zero temperature and the gap as a function of temperature in the disordered paramagnetic phase.     

Magnetoelastic excitations in ferromagnets with cubic single-ion anisotropy

Magnetic and elastic properties of three-axial (S=2) ferromagnets with single-ion anisotropy have been discussed. The phase diagram in the plane (single-ion anisotropy, temperature) has been constructed and two tricritical points driven by the magnetoelastic interactions have been found. The dispersion of the magnetoelastic excitations in the low temperature has been considered. The special attention has been given to the systems with single-ion anisotropy constantK–8 where the softening of a magnetoelastic mode can be observed.     

Stochastic resonance in single-domain nanoparticles with cubic anisotropy

The signal-to-noise ratio for magnetic stochastic resonance in a superparamagnetic particle with cubic anisotropy is shown to be strongly dependent on the Larmor precession damping α. This phenomenon is due to the coupling of the relaxation and precession modes and can be used for measuring α. The dependence of the signal-to-noise ratio on α is characteristic of particles with nonaxial anisotropy; so the effect is absent in uniaxial particles.     

Temperature dependence of ferromagnetic anisotropy energy in cubic crystals

The magnetic anisotropy constant K₁ for cubic ferromagnetic crystals has been discussed based on the general expressions derived by Yang for hexagon crystals. By matching the experimental data, we obtained

$\text{K}{}_1\text{(T,H)}\text{K}{}_1\text{(0,0)}\text{=?6.14}\text{I}\text{?}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{(T,H) + 3.36}\text{I}\text{?}\text{9}\text{2}\text{(T,H) + 4.88m}{}^2\text{(T,H) ?1.10[}\text{I}\text{?}\text{5}\text{2}\text{(T,H)]}{}^2$

for nickel, and $\text{K}{}_1\text{(T,H)/K}{}_1\text{(0,0)=I}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ for iron, where Î_{$\text{5}\text{2}$} and Î_{$\text{9}\text{2}$} are the hyperbolic bessel functions of order 2 and 4 respectively and m is the reduced magnetization. Both expressions have a theoretical basis.     

Orientational transitions in a simple system with configurations anisotropy

Using the example of a linear chain with periodically distributed impurity ions, we study the basic features of orientational transitions in systems with configurational anisotropy. The possibility of orientational transitions due to a relative change in the magnitudes of the anisotropy and exchange energies with no difference in the signs of the anisotropy constants for impurity ions and ions of the matrix system is pointed out. Phase diagrams for the system in an external magnetic field are constructed.Translated form Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 84–89 April, 1985.The authors thank A. V. Deryagin for useful discussions of the results.     

Surface anisotropy tensors for cubic and hcp ferromagnets

Point groups of the plane surfaces of cubic and h.c.p. ferromagnets are indicated together with the corresponding forms of the first and second rank surface anisotropy tensors.     

Crossover behavior of anisotropic cubic system with ionic anisotropy

Crossover behavior of anisotropic cubic N-component spin system with ionic anisotropies of different magnitude is studied in terms of the renormalization-group (RG) approach in momentum space. As a fundamental case, we choose a system with two kinds of strength of ionic anisotropies (i.e. m²₁ for the M-component spin and m²₂ for the other (N–M)-one), which has a bicritical point. We discuss the critical behavior and crossover behavior between the M- component system and the N-component system on the critical exponents [i.e., coefficient functions appearing in the RG equation of γS for the spin field S, γS² for the S²-field and γδS² for the δS² (≡[(N-M)S²₂-MS²₂]/N)-field] and on the temperature-dependent crossover exponent γeff.     

Longitudinal dynamic susceptibility of superparamagnetic particles with cubic anisotropy

We study the linear response of a system of single-domain ferromagnetic particles with cubic magnetic anisotropy to a weak external a.c. magnetic field. By averaging the Gilbert equation with a fluctuating field for the magnetization of an individual particle we derive a system of recurrence equations for the spectra of equilibrium correlation functions describing the longitudinal relaxation of the system. We find the solution of this system by using matrix continued fractions. We also evaluate the longitudinal relaxation time and the spectrum of the complex-valued magnetic susceptibility. Finally, we show that the nature of susceptibility dispersion is determined by the anisotropy and dissipation parameters. Zh. éksp. Teor. Fiz. 115, 101–114 (January 1999)     

Magnetic states of small cubic particles with uniaxial anisotropy

The lowest energy states in small cubic particles with uniaxial anisotropy are explored as a function of anisotropy strength and particle size. The investigations result in a phase diagram which contains the boundaries between the regions of one, two and three domains (flower, vortex and double vortex states). While the general features of the phase diagram are derived from energy estimates based on domain theory, the details are obtained using numerical micromagnetics. The two-domain and the three-domain phase can be subdivided into subphases. The comparison between different configurations revealed that a twisted vortex configuration with an S-shaped domain wall replaces the symmetric vortex with a straight wall at larger sizes. The three-domain phase contains two subphases which are symmetric with respect to (1 0 0) and (1 1 0) mirror planes, respectively. The transition from two to three domains occurs into the (1 1 0)-three-domain-state (diagonal state). This structure can be described as a configuration with two (quarter-) circular domain walls in two opposing corners. However, this configuration is energetically favored only in a small region within the phase diagram relative to the (1 0 0)-symmetry three-domain state with straight walls (sandwich state).     

Inhomogeneous configurations of magnetization of ferromagnetic films with biaxial anisotropy

The system of the Landau-Lifshitz equations and magnetostatic equations for a ferromagnetic film with biaxial anisotropy and a Q-factor smaller than unity is reduced to a single scalar equation for the magnetostatic potential. Such a procedure is possible if the magnetization modulation scale in the sample considerably exceeds the characteristic magnetic length. The solutions to this equation describing inhomogeneous periodic magnetic configurations are obtained. The energy analysis of these configurations is carried out.     

Axial and diagonal anisotropy crossover exponents for cubic systems

Cubic n-component spin systems exhibit two distinct quadratic spin anisotropy crossover exponents, appropriate for axial and diagonal anisotropies. Results for n→∞ and to order ?², and for nm-component systems are given, and relevance to multi-critical points in various systems is discussed.