Nature of the field-induced magnetic incommensurability in multiferroic Ni$_3$TeO$_6$

TL;DR

This study investigates the magnetic phase transition in Ni$_3$TeO$_6$ under high magnetic fields, revealing a shift from a collinear antiferromagnetic structure to a conical spiral, and clarifies the underlying mechanism behind its magneto-electric coupling.

Contribution

The paper provides the first detailed neutron scattering analysis of the field-induced incommensurate magnetic structure in Ni$_3$TeO$_6$, identifying the phase transition nature and ruling out inverse Dzyaloshinskii-Moriya interaction as the cause.

Findings

Magnetic structure transitions from commensurate to incommensurate spiral above 8.6 T.

First-order phase transition evidenced by discontinuous change in ordering vector.

Spin wave gap minima align with incommensurate propagation vector.

Abstract

Using single crystal neutron scattering we show that the magnetic structure Ni$_3$TeO$_6$ at fields above 8.6 T along the $c$ axis changes from a commensurate collinear antiferromagnetic structure with spins along c and ordering vector $Q_C$= (0 0 1.5), to a conical spiral with propagation vector $Q_{IC}$= (0 0 1.5$\pm\delta$),$\delta\sim$0.18, having a significant spin component in the ($a$,$b$) plane. We determine the phase diagram of this material in magnetic fields up to 10.5 T along $c$ and show the phase transition between the low field and conical spiral phases is of first order by observing a discontinuous jump of the ordering vector. $Q_{IC}$ is found to drift both as function of magnetic field and temperature. Preliminary inelastic neutron scattering reveals that the spin wave gap in zero field has minima exactly at $Q_{IC}$ and a gap of about 1.1 meV consisting with a cross-over around 8.6 T. Our findings excludes the possibility of the inverse Dzyaloshinskii-Moriya interaction as a cause for the giant magneto-electric coupling earlier observed in this material and advocates for the symmetric exchangestriction as the origin of this effect.