Ordered States and Nonlinear Large-Scale Excitations in a Plane Magnet with Spin s=1

TL;DR

This paper investigates ordered states and topological excitations in a quasi-two-dimensional spin-1 magnet with biquadratic interactions, proposing effective Hamiltonians that describe large-scale excitations affecting long-range order.

Contribution

It introduces two effective Hamiltonians for large-scale excitations in a 2D spin-1 magnet, highlighting their role in topological excitations and order destruction.

Findings

Effective Hamiltonians describe nematic and mixed phases.

Topological excitations can emerge at low temperatures.

These excitations can disrupt long-range magnetic order.

Abstract

We study ordered states and topological excitations in a quasi-two-dimensional magnet, modeled by a square lattice with spins $s {=} 1$ at all sites, and the Hamiltonian with biquadratic exchange interaction between nearest neighbor sites. We propose two effective Hamiltonians for description of large-scale excitations in the two-dimensional case. They describe excitations of the mean field in a nematic phase and a mixed ferromagnetic-nematic phase. It is shown that the effective Hamiltonians are minimized on configurations with fixed topological charge. These topological excitations can arise at low temperatures and cause a destruction of a long-range order in the two-dimensional system.