Incommensurate phases in ferromagnetic spin-chains with weak antiferromagnetic interchain interaction

TL;DR

This paper investigates the complex magnetic phases in ferromagnetic spin chains with weak antiferromagnetic interchain and dipole interactions, revealing how the ground state and spin order depend on interaction strengths and magnetic field orientation.

Contribution

It provides a detailed analysis of the phase diagram and incommensurate phases in ferromagnetic spin chains considering dipole and interchain interactions, including field orientation effects.

Findings

Ground state varies from ferromagnetic to incommensurate with increasing ppa.

Incommensurate phases exhibit continuous wave vector changes with field rotation.

The structure of spin order is highly sensitive to magnetic field direction.

Abstract

We study planar ferromagnetic spin-chain systems with weak antiferromagnetic inter-chain interaction and dipole-dipole interaction. The ground state depends sensitively on the relative strengths of antiferromagnetic exchange and dipole energies kappa=J'a^2c/(g_L\mu_B)^2. For increasing values of \kappa, the ground state changes from a ferromagnetic via a collinear antiferromagnetic and an incommensurate phase to a 120^o structure for very large antiferromagnetic energy. Investigation of the magnetic phase diagram of the collinear phase, as realized in CsNiF_3, shows that the structure of the spin order depends sensitivly on the direction of the magnetic field in the hexagonal plane. For certain angular domains of the field incommensurate phases appear which are separated by commensurate phases. When rotating the field, the wave vector characterizing the structure changes continuously in the incommensurate phase, whereas in the commensurate phase the wave vector is locked to a fixed value describing a two-sublattice structure. This is a result of the competition between the exchange and the dipole-dipole interaction.