Axial quadrupole phase of a uniaxial spin-1 magnet

TL;DR

This paper investigates the uniaxial phase of a spin-1 magnet with quadrupole order, analyzing how anisotropies and external fields influence phase boundaries, excitation spectra, and critical temperatures.

Contribution

It provides a theoretical analysis of the axial quadrupole phase considering general anisotropic interactions and derives conditions for phase boundaries and excitation spectra.

Findings

Magnetization in the molecular field approximation is temperature-independent and linearly dependent on the magnetic field.

Two branches of the spin excitation spectrum are derived.

The phase transition boundary is influenced by anisotropy constants of the biquadratic exchange.

Abstract

Uniaxial phase of the axial quadrupole spin-1 magnet in an external magnetic field is investigated. A case where the system includes single-ion anisotropy and anisotropic biquadratic exchange interaction the most general form, is considered. It is proved, that the molecular field approximation of the relative magnetization does not depend on temperature and increases linearly with the external magnetic field. Two branches of the spin excitation spectrum are derived. Condition of mitigation of the spectrum defines the boundary between the axial quadrupole and angular phases. The critical temperature of the corresponding phase transition depends considerably on the anisotropy constants of the biquadratic exchange interaction.