Phase transitions of the ferroelectric $(\mathrm{ND}_4)_2\mathrm{FeCl}_5\cdot\mathrm{D}_2\mathrm{O}$ under a magnetic field

TL;DR

This study models the complex magnetic and ferroelectric phase transitions of $( ext{ND}_4)_2 ext{FeCl}_5 ext{·D}_2 ext{O}$ under magnetic fields, highlighting the role of high-order spin interactions and predicting a new ferroelectric phase.

Contribution

The paper introduces a spin model with high-order onsite spin anisotropic interactions that accurately captures phase transitions and harmonic components in this multiferroic material.

Findings

Successful modeling of ferroelectric phase transitions under magnetic field.

Prediction of a new ferroelectric phase between FE II and FE III.

Demonstration of the importance of high-order spin anisotropic interactions.

Abstract

Due to the strong coupling between magnetism and ferroelectricity, $(\mathrm{ND}_4)_2\mathrm{FeCl}_5\cdot\mathrm{D}_2\mathrm{O}$ exhibits several intriguing magnetic and electric phases. In this letter, we include high-order onsite spin anisotropic interactions in a spin model that successfully captures the ferroelectric phase transitions of $(\mathrm{ND}_4)_2\mathrm{FeCl}_5\cdot\mathrm{D}_2\mathrm{O}$ under a magnetic field and produces the large weights of high-order harmonic components in the cycloid structure that are observed from neutron diffraction experiments. Moreover, we predict a new ferroelectric phase sandwiched between the FE II and FE III phases in a magnetic field. Our results emphasize the importance of the high-order spin anisotropic interactions and provide a guideline to understand multiferroic materials with rich phase diagrams.