Alternating commensurate-incommensurate structures in the magnetic phase diagram of CsNiF3

TL;DR

This paper investigates the magnetic phase diagram of CsNiF3, revealing incommensurate phases under certain magnetic field orientations and analyzing phase transitions using linear spin-wave theory.

Contribution

It provides the first detailed prediction of incommensurate phases and the instability line in CsNiF3 based on spin-wave theory and field orientation.

Findings

Incommensurate phases are predicted for fields perpendicular to the chains.

The instability line of the paramagnetic phase is mapped as a function of field strength and direction.

The system transitions between commensurate and incommensurate phases depending on magnetic field orientation.

Abstract

The magnetic phase diagram of the quasi one-dimensional spinchain system CsNiF$_3$ below the N\'eel temperature is determined. For magnetic fields perpendicular to the spin chains incommensurate phases are predicted. From linear spin-wave theory we obtain the instability line of the paramagnetic phase as a function of the strength and the direction of the field. The system undergoes a transition to a commensurate or an incommensurate phase depending on the direction of the magnetic field. In the commensurate phase the characterizing wave vector is locked to values describing a two-sublattice structure, whereas in the incommensurate phase the wave vector changes continuously between the corresponding two-sublattice wave vectors.