Spin fluctuations in the stacked-triangular antiferromagnet YMnO3

TL;DR

This study investigates spin fluctuations in YMnO3 above its Neel temperature using neutron scattering, revealing distinct in-plane and out-of-plane excitation behaviors and providing insights into the magnetic dynamics of this triangular antiferromagnet.

Contribution

First detailed analysis of spin fluctuation spectrum in YMnO3 above Neel temperature using polarized neutron scattering.

Findings

In-plane excitation has a central peak and Debye-like contribution.

Quasi-elastic fluctuations exhibit a linewidth increasing with q, with dynamical exponent z=2.3.

Out-of-plane fluctuations have a gap at the magnetic zone center.

Abstract

The spectrum of spin fluctuations in the stacked-triangular antiferromagnet YMnO3 was studied above the Neel temperature using both unpolarized and polarized inelastic neutron scattering. We find an in-plane and an out-of-plane excitation. The in-plane mode has two components just above TN, a resolution-limited central peak and a Debye-like contribution. The quasi-elastic fluctuations have a line-width that increases with q like Dq^z and the dynamical exponent z=2.3. The out-of-plane fluctuations have a gap at the magnetic zone center and do not show any appreciable q-dependence at small wave-vectors.