Magnetic Order and Spin Dynamics in Ferroelectric HoMnO$_{3}$

TL;DR

This study investigates the magnetic order and spin dynamics in the multiferroic HoMnO$_{3}$, revealing detailed spin wave behavior, magnetic phase transitions, and the coupling between ferroelectricity and magnetism.

Contribution

It provides new neutron scattering data and analysis of spin wave dispersion and magnetic phases in HoMnO$_{3}$, highlighting the coupling between magnetic and ferroelectric order parameters.

Findings

Spin wave dispersion is well described by a 2D Heisenberg model with specific exchange and anisotropy parameters.

Magnetic structures and phase diagram are mapped, showing additional low-temperature magnetic transitions.

Ho$^{3+}$ ions exhibit magnetic ordering below 8 K, indicating complex magnetic interactions.

Abstract

Hexagonal HoMnO$_{3}$ is a frustrated antiferromagnet (T$_{N}$=72 K) ferroelectric (T$_{C}$=875 K) in which these two order parameters are coupled. Our neutron measurements of the spin wave dispersion for the S=2 Mn$^{3+}$ on the layered triangular lattice are well described by a two-dimensional nearest-neighbor Heisenberg exchange J=2.44 meV, and an anisotropy $D$ that is 0.093 meV above the spin reorientation transition at 40 K, and 0.126 meV below. For $H\parallel c$ the magnetic structures and phase diagram have been determined, and reveal additional transitions below 8 K where the ferroelectrically displaced Ho$^{3+}$ ions are ordered magnetically.