Magnon relaxation in a spin nematic

Abstract

Magnon relaxation processes in the nematic phase of a magnet with spin S=1 are investigated for a general form of the isotropic exchange interaction, including bilinear and biquadratic interactions in respect to the site spin operators. The temperature dependence and momentum dependence of the magnetic decrement are found in the long-wavelength approximation. It is shown that the elementary excitations in a spin nematic (magnons) have all the properties of Goldstone excitations; in the limit of small wave vectors they have a linear dispersion law, while the damping is quadratic in the wave vector. The similarity of magnon behavior in a spin nematic to that in an antiferromagnet is noted.

Effect of tilted anisotropy on spin states of strongly anisotropic 2D film

“…This leads to the diagonalization of the quadrupole order parameter tensor ( = 0); in this case, the geometrical image of the quadrupole phase is an infinitely thin disk in the xy plane of the turned sys tem of coordinates [24]. After this unitary transforma tion, the constants of effective single ion anisotropies in the quadrupole phase have the form and = 0.…”

“…After this unitary transforma tion, the constants of effective single ion anisotropies in the quadrupole phase have the form and = 0. In this case, one site Hamiltonian (3) assumes the simpler form (24) As before, we analyze the system at temperatures much lower than the Curie temperature. Solving the one site problem with Hamiltonian (24), we obtain the energy levels of a magnetic ion in the quadrupole phase and the eigenfunctions of Hamiltonian (24) as follows:…”

Dynamic and static properties of rigidly fixed ultrathin ferromagnetic films with S = 1 and competing anisotropies

“…In the case of strong single-ion anisotropy, it is possible for the magnetization to go entirely to zero when a ferromagnetic exchange interaction is present. 31,47 The most distinct manifestation of this effect is the appearance, in magnets with a spin of one, of a quadrupole phase (spin nematic phase [50][51][52][53] ) characterized by zero average spin at a site even for zero temperature. The symmetry of the quadrupole phase is greater than for any other magnetically ordered state, since the symmetry group of this state includes the operation of time reflection.…”

“…It should be noted that the quadrupole state may develop not only because of a large single-ion anisotropy, but also in connection with higher spin invariants such as a biquadratic exchange interaction for magnets with S ¼ 1. [49][50][51][52][53][54] This paper is a study of the properties of ultrathin magnetic films with different relationships between the exchange interaction energies and the single-ion interaction energies. We assume that the film has a thickness equal to one atomic layer, i.e., is a 2D object, and has a flat, square lattice.…”

Dynamic properties of magnets with spin S = 3/2 and non-Heisenberg isotropic interaction

“…Thus, the nematic states for spin S = 1 have been studied fairly extensively: the interactions of elemen tary excitations and the relaxation processes were investigated for them [19,[33][34][35][36], and nonlinear exci tations, solitons, were found [37][38][39][40]. Both one dimensional solitons [37,38] that resemble the Lieb states of a nonideal Bose gas [41] discovered many years ago and topological two dimensional solitons [39,40] were obtained.…”