Magnetic order, spin waves and fluctuations in the triangular antiferromagnet La2Ca2MnO7

TL;DR

This study investigates the magnetic properties and spin dynamics of La2Ca2MnO7, revealing two-dimensional magnetic order, spin-wave excitations, and persistent fluctuations above the ordering temperature.

Contribution

It provides a comprehensive analysis combining susceptibility, specific heat, muSR, and neutron scattering data to characterize magnetic order and excitations in a triangular antiferromagnet.

Findings

Magnetic order develops below 2.8 K with a   magnetic structure.

Exchange interactions and spin-wave gap are quantitatively estimated from experiments.

Persistent spin dynamics and short-range correlations are observed above T_N.

Abstract

We report magnetic susceptibility, specific heat and muon spin relaxation (muSR) experiments on the triangular antiferromagnet La2Ca2MnO7 which develops a genuine two-dimensional, three-sublattice \sqrt{3} \times \sqrt{3} magnetic order below T_N = 2.8 K. From the susceptibility and specific heat data an estimate of the exchange interaction is derived. A value for the spin-wave gap is obtained from the latter data. The analysis of a previously reported inelastic neutron scattering study yields values for the exchange and spin-wave gap compatible with the results obtained from macroscopic measurements. An appreciable entropy is still missing at 10 K that may be ascribed to intense short-range correlations. The critical paramagnetic fluctuations extend far above T_N, and can be partly understood in terms of two-dimensional spin-wave excitations. While no spontaneous muSR field is observed below T_N, persistent spin dynamics is found. Short-range correlations are detected in this temperature range. Their relation to a possible molecular spin substructure and the observed exotic spin fluctuations is discussed.