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It is shown that the magnons in a ferromagnetic chain can turn into "solitary magnons" pmpagating without smearing along the chain with constant velocity smaller than the sound velocity in such media.

As ist has been shown in /1, 2/ the solitary magnons can exist in some ferromagnetic chains. In /1/ the solitary magnons can exist as a bound state of a spin deviation and the deformation caused by this. In /2/ the soliton solution appears as a consequence of the magnon-magnon interaction. Such soliton solutions are closely related to the presence of a magnetic anisotropy. The results obtained in /2/ a r e based on the Holstein-Primakoff representation of the spin operators and by using Glauber's coherent states which give a good result for large spins.In the present paper we discuss some properties of the solitary magnon states (we shall name them "magnolitons") and give a quasi-classical interpretation of these states. W e start from the Heisenberg Hamiltonian +where Z is the magnetic field, p is the magnetic moment, S. are the spin cyclic components, J and 2 are the exchange integrals, j labels the lattice site, and d runs over the nearest neighbours of j . 1As it was shown in /2/, the Holstein-Primakoff representation of spin operators + by means of Bose operators a and a and Glauber's coherent states ({cY1} > ET lal >, satisfying the equations /3/ leads in the continuum limit ( a (t)-a(x, t ) ) to the equationThe nonlinear Schrodinger equation (3) has a normalized to n solution 1/2 exp ( i( T X -ro -w n t) ) sech ("-yt). (4) where a=fiv/2 J S , nl: = 2 JS/($ -J), which shows that fi w is the energy change of the n-magnoliton state by adding one more magnoliton. n Looking at the last formula in (2) we obtain where <. . .> is taken over the coherent states. Short Notes K91 Equations (4) and ( 8 ) show that the magnoliton can move and transfer magnetic moment (the whole magnetic moment transferred is p n). We can consider the magnoliton as a new (flcondensate-likeff) phase state due to the spin correlation in a macroscopic region with length t . Then obviously fi w plays the role of a chemical potential and m(x, t) can be treated as a complex order parameter which plays the role of a classical Schriidinger field. n As it was pointed by Langer /4/ , thevalidity of the classical description for many-boson systems implies "superfluidityfl. In the case discussed a quasi-classical limit of our system can be expressed a s where H is the Hamiltonian (1) in the continuum approximation. In the action-angle variables Jy = a*=, 0 = (1/21) ln(a/olL) we have "which a r e just the superfluidity equations of motion discussed by Anderson /5/. Using (4), the current of the magnetic moment density is j (x, t) -la1 v. If t-. 00 the soliton solution (4) disappears and we have the well-known homogeneous state of the ferromagnetic chain. 2We would like to give one more quasi-classical picture of the problem discussed. It is worth noting that (3) can be obtained by using Dyson-Maleev's transformation instead of (2).In the three-dimensional ferromagnet, the procedure above leads to the equationwhich has a corresponding to n-magnoliton state solution .and, of course, cannot be normalized t o n. The normalization can be done as usual i...

SummaryExperimental and theoretical data are presented that relate to strip waveguides obtained by applying a voltage to electrodes deposited on a Ti:LiNbO

Defecton Diffusion in the Very Quantum Region B Y D.I. PUSHKAROV and KH.1. PUSHKAROV K97 A t sufficiently low temperatures the activation mechanism of the diffusion of point defects in quantum crystals is replaced by the quantum diffusion of the corresponding quasi-particlesdefectons (references (1), (2)). Furthermore, one dfi T * If the temperature is so low that 1 > L we have 1 3 6 D = -Lvx0.58 La KlOO physica status solidi (b) 74But one must keep in mind that a t sufficiently low temperatures the majority of the defectons will be in the Bose-Einstein condensate. Then, small changes in the chemical potential can cause a directed stream of the condensate and this effect can predominate over the diffusion motion.

The existence of solitary bound states of spin deviations and lattice deformation created byEs wird die Existenz von gebundenen Zustinden zwischen der Spinanregung und der Gitter-them in some ferromagnetic systems with biquadratic exchange is shown. deformation in einigen Ferromagneten mit biquadratischem Austausch gezeigt.

At the absolute zero of temperature a crystal with a point defect (vacancy, -impurity, etc.) i s not in its ground state. One can see this even only because of the fact that the energy of such a crystal i s degenerate with respect to the crystal defect position.In quantum crystals in which the amplitude of the zero-point motion of the a t o m about the equilibrium lattice sites is large enough, the point defects must delocalize themselves and t u r n into quasi-particles -defectons (1, 2). The characteristic time of that process and the delocalization wave velocity must determine the diffusion coefficient of the defects at T = 0.Let us coneider the delocalization process of an individual point defect. To this effect we shall t u r n to the Schriidinger equation ifi-= ~y a t and will try to find such a solution y (x, t) which at the moment t = 0 coincides with the function -(x), describing the crystal state with a localized defect in the lattice site ? . 9As it was shown in (2) we can take as eigdunctions of the Hamiltonian Hence, the solutions of the equation (1) must have the form where 6w(z) = c (2) i s the defecton dispersion law.Then the function we look for can be written in the form w+x, t) = JG(x. 5. t) Y ; ( CF I d a