Rich magnetoelectric phase diagrams of multiferroic single-crystal alpha-NaFeO2

TL;DR

This study maps detailed magnetic and ferroelectric phase diagrams of alpha-NaFeO2, revealing multiple ordered phases and elucidating the mechanisms behind its multiferroic behavior through experimental and theoretical analysis.

Contribution

It provides comprehensive magnetic field versus temperature phase diagrams and explains polarization directions using an extended inverse Dzyaloshinskii-Moriya mechanism, incorporating exchange interactions up to fourth-nearest neighbors.

Findings

Identified five and six magnetically ordered phases in different field directions.

Demonstrated the role of competing antiferromagnetic interactions in phase diagram complexity.

Explained polarization directions via an extended inverse Dzyaloshinskii-Moriya mechanism.

Abstract

The magnetic and dielectric properties of the multiferroic triangular lattice magnet compound alpha-NaFeO2 were studied by magnetization, specific heat, dielectric permittivity, and pyroelectric current measurements and by neutron diffraction experiments using single crystals grown by a hydrothermal synthesis method. This work produced magnetic field (in the monoclinic ab-plane, B_ab, and along the c*-axis, B_c) versus temperature magnetic phase diagrams, including five and six magnetically ordered phases in B_ab and along B_c, respectively. Comparing the polarization direction to the magnetic structures in the different ferroelectric phases, we conclude that the extended inverse Dzyaloshinskii-Moriya mechanism expressed by the orthogonal components p1 ~ rij x (Si x Sj ) and p2 ~ Si x Sj can explain the polarization directions. Based on calculations incorporating exchange interactions up to fourth-nearest-neighbor (NN) couplings, we infer that competition among antiferromagnetic second NN interactions in the triangular lattice plane, as well as weak interplane antiferromagnetic interactions, are responsible for the rich phase diagrams of alpha-NaFeO2.