Inelastic Neutron Scattering in Weakly Coupled Triangular Spin Tubes CsCrF$_4$

TL;DR

This study uses inelastic neutron scattering to investigate spin dynamics in CsCrF$_4$, revealing consistent spin Hamiltonian parameters across phases and suggesting an order-by-disorder mechanism for phase transitions.

Contribution

It provides detailed experimental and theoretical analysis of spin interactions in CsCrF$_4$, identifying the Hamiltonian and revealing identical spectra in different phases despite structural differences.

Findings

Spin Hamiltonian includes intertube, Dzyaloshinskii-Moriya, and anisotropy terms.

Spectra in IT and LT phases are identical, indicating no change in Hamiltonian.

Phase transitions likely driven by order-by-disorder mechanism.

Abstract

We performed inelastic neutron scattering (INS) experiments to measure spin dynamics on a polycrystalline sample of a spin tube candidate CsCrF$_{4}$. The compound exhibits a successive phase transition from a paramagnetic phase through an intermediate temperature (IT) phase of a 120$^{\circ}$ structure to a low temperature (LT) phase of another 120$^{\circ}$ structure. Elaborate comparison between observed and calculated neutron spectra in LT phase reveals that the spin Hamiltonian is identified as antiferromagnetic spin tubes including perturbative terms of intertube interaction, Dzyaloshinskii-Moriya interaction, and single ion anisotropy. A phase diagram for the ground state is classically calculated. A set of parameters in the spin Hamiltonian obtained from the INS spectra measured in LT phase is quite close to a boundary to the phase of the 120$^{\circ}$ structure of IT phase. The INS spectra measured in IT phase is, surprisingly, the same as those in LT phase in the level of powder averaged spectra, even though the magnetic structures in IT and LT phases are different. Identical dynamical structures compatible with two different static structures are observed. No difference in the observed spectra indicates no change of the spin Hamiltonian with the temperature, suggesting that the origin of the successive phase transition being order-by-disorder mechanism.