Unconventional spin fluctuations in the hexagonal antiferromagnet YMnO$_3$

TL;DR

This study reveals unconventional spin fluctuations in YMnO₃, showing coexistence of long-lived spin-waves and a central peak indicating 2D antiferromagnetic fluctuations, highlighting complex magnetic dynamics below the Néel temperature.

Contribution

It provides new insights into the spin dynamics of YMnO₃, demonstrating coexistence of different fluctuation time scales and suggesting competition between magnetic phases.

Findings

Presence of a central peak indicating 2D antiferromagnetic fluctuations

Coexistence of long-lived spin-waves and fast fluctuations

Evidence of competition between Ne9el and Kosterlitz-Thouless phases

Abstract

We used inelastic neutron scattering to show that well below its N\'{e}el temperature, $T_{\rm N}$, the two-dimensional (2D) XY nearly-triangular antiferromagnet YMnO$_{3}$ has a prominent {\it central peak} associated with 2D antiferromagnetic fluctuations with a characteristic life time of 0.55(5) ps, coexisting with the conventional long-lived spin-waves. Existence of the two time scales suggests competition between the N\'{e}el phase favored by weak interplane interactions, and the Kosterlitz-Thouless phase intrinsic to the 2D XY spin system.