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

• Published in: arXiv.org 2015-07
• Main Authors: P Dalmas de Réotier, Marin, C, Yaouanc, A, Douce, T, Sikora, A, Amato, A, Baines, C
• Format: Article
• Language: English
• Subjects: Antiferromagnetism; Heat exchange; Inelastic scattering; Magnetic permeability; Magnons; Muon spin relaxation; Neutron scattering; Neutrons; Specific heat; Spin dynamics; Substructures; Variation
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1507.01740

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.